To look at the various aspects of your question from a Catholic point of view...
If one's entry into the church is solemnized by baptism...
What does the Catholic Church teach about baptism?
1213 Holy Baptism is the basis of the whole Christian life, the
gateway to life in the Spirit (vitae spiritualis ianua), 4 and the
door which givesaccessto theother sacraments. Through Baptism we are
freed from sin and reborn as sons of God; we become members of Christ,
are incorporated into the Church and made sharers in her mission:
"Baptism is the sacrament of regeneration through water in the word." (1)
Does this indelable mark protect a person from willingly and knowingly removing his or herself from what the Church defines as the Body of Christ (a.k.a. the Bride of Christ, a.k.a. the Church universal)? No.
1463 Certain particularly grave sins incur excommunication, the most
severe ecclesiastical penalty, which impedes the reception of the
sacraments and the exercise of certain ecclesiastical acts, and for
which absolution consequently cannot be granted, according to canon
law, except by the Pope, the bishop of the place or priests authorized
by them. In danger of death any priest, even if deprived of faculties
for hearing confessions, can absolve from every sin and
...then how does one leave the church?
What exactly is excommunication?
Excommunication (Latin ex, out of, and communio or communicatio,
communion — exclusion from the communion), the principal and severest
censure, is a medicinal, spiritual penalty that deprives the guilty
Christian of all participation in the common blessings of
ecclesiastical society. Being a penalty, it supposes guilt; and being
the most serious penalty that the Church can inflict, it naturally
supposes a very grave offence. It is also a medicinal rather than a
vindictive penalty, being intended, not so much to punish the culprit,
as to correct him and bring him back to the path of righteousness. It
necessarily, therefore, contemplates the future, either to prevent the
recurrence of certain culpable acts that have grievous external
consequences, or, more especially, to induce the delinquent to satisfy
the obligations incurred by his offence. Its object and its effect are
loss of communion, i.e. of the spiritual benefits shared by all the
members of Christian society; hence, it can affect only those who by
baptism have been admitted to that society. Undoubtedly there can and
do exist other penal measures which entail the loss of certain fixed
rights; among them are other censures, e.g. suspension for clerics,
interdict for clerics and laymen, irregularity ex delicto, etc.
Excommunication, however, is clearly distinguished from these
penalties in that it is the privation of all rights resulting from the
social status of the Christian as such. The excommunicated person, it
is true, does not cease to be a Christian, since his baptism can never
be effaced; he can, however, be considered as an exile from Christian
society and as non-existent, for a time at least, in the sight of
ecclesiastical authority. But such exile can have an end (and the
Church desires it), as soon as the offender has given suitable
satisfaction. Meanwhile, his status before the Church is that of a
stranger. He may not participate in public worship nor receive the
Body of Christ or any of the sacraments. Moreover, if he be a cleric,
he is forbidden to administer a sacred rite or to exercise an act of
If we consider only its nature, excommunication has no degrees: it
simply deprives clerics and laymen of all their rights in Christian
society, which total effect takes on a visible shape in details
proportionate in number to the rights or advantages of which the
excommunicated cleric or layman has been deprived. The effects of
excommunication must, however, be considered in relation also to the
rest of the faithful. From this point of view arise certain
differences according to the various classes of excommunicated
persons. These differences were not introduced out of regard for the
excommunicated, rather for the sake of the faithful. The latter would
suffer serious inconveniences if the nullity of all acts performed by
excommunicated clerics were rigidly maintained. They would also be
exposed to grievous perplexities of conscience if they were strictly
obliged to avoid all intercourse, even profane, with the
excommunicated. Hence the practical rule for interpreting the effects
of excommunication: severity as regards the excommunicated, but
mildness for the faithful. We may now proceed to enumerate the
immediate effects of excommunication. They are summed up in the two
well known verses:
Res sacræ, ritus, communio, crypta, potestas, prædia sacra, forum,
civilia jura vetantur,
i.e. loss of the sacraments, public services and prayers of the
Church, ecclesiastical burial, jurisdiction, benefices, canonical
rights, and social intercourse. (3)
Can a Catholic just stop going to Mass or replace attendance with any other weekly denominational worship?
2181 The Sunday Eucharist is the foundation and confirmation of all
Christian practice. For this reason the faithful are obliged to
participate in the Eucharist on days of obligation, unless excused for
a serious reason (for example, illness, the care of infants) or
dispensed by their own pastor.119 Those who deliberately fail in this
obligation commit a grave sin. (4)
Is there a way to leave the Church on good terms?
The answer to that question is that it is impossible to leave the Roman Catholic Church on good terms - with one exception.
Many people do not know that the Roman Catholic Church is not the only Catholic Church. There are many Eastern Catholic Churches, and it is absolutely possible for a Roman Catholic to become a member of any of these churches. The usual requirement to switch is that a person attends an Eastern liturgy for at least 2 years, and both Bishops approve. It should be noted however, that these churches are still in union with the Pope, and it is still a requirement to adhere to church teaching.
It is possible for a person to leave a local church and transfer membership to another church for any legitamate reason (i. e. relocation, lack of youth ministry, etc.).
To summarize - Is it possible for a Catholic to leave a church on good terms? Yes.
Is is possible for a Catholic to leave the Church on good terms? No.
At "best," this would result in grave sin, and at worst being publically reprimanded. Its important to note that there are many gray areas with no one size fits all case.