The Qur’an says that he (AS) will die, but the verse in particular also confirms other things:
**“And peace is on me the day I was born and the day I will die and the day I am raised alive.” Surah Maryam Verse 33
**Note in this blessed verse the actual word “mawt” is indeed used … Also note that this word “peace” is being uttered in a sense that means “no physical or psychological harm” - shall come to Isa (AS). And this interpretation is supported by various commentators. At-Tabari to be specific.
Was Isa (AS) successful - well of course he was - his mission was to teach the tribes the correct understanding - he did so in the most amazing way - but Allah (SWT) didn’t give them tawfiq to apply his teachings on account of their corruption. Isa (AS) hence was always going to pave the way for RasoolAllah (SAW) and that is why he came first time to give glad tidings of Muhammad (SAW) also to warn the Jewish tribes about this and that he will return to kill the Dajjal. He knew the Dajjal would not appear until the final prophet (SAW) has come and gone. It was always meant to be that Isa (AS) was to return.
Now as per your reasoning - if humans can to some extent do things to slow time down, or use chemicals or temperature to slow down aging - then why can’t Allah (SWT) do the same or something similar but more profound?