United Pentecostals do not deny that there is a Father and there is a Son. They believe the Father and Son are one Spirit. They believe that there is a distinction between Father and Son. The Son is God in the Flesh. The Father is God not in the flesh. The United Pentecostals point out that in Scripture, the term "Son" is always used in reference to God in the flesh. If you would like to read more of what the UPC doctrine is, I suggest "The Oneness of God," by David Bernard. (I am not UPC, thus, I hesitate to go any further specifically regarding their doctrine, lest I misrepresent them).
As a Oneness adherent, I would continue thus in regard to this verse and your question:
Flesh is mortal, spirit is not. Flesh can suffer, flesh can die, the spirit experiences the suffering of the body, but the spirit does not die; Thus, When Christ died on the cross, God did not die. Note:
46 Then Jesus, calling out with a loud voice, said, "Father, into your hands I commit my spirit!" And having said this he breathed his last (NKJV). /"gave up the ghost" (KJV).
So, God did come in the flesh, and did experienced death in the Body he took on; He suffered, and in the sense that any man dies, he died. But God (Spirit) did not die.