I had to wuit a run to go do something, i was having one of the greatest runs of my life, it was on my phone, am i allowed to screen record later and finish the run or would it be invalid?

Any runs that are not played in the All Achievements category has to be played in 1 session, meaning that you can't put runs in 2 or more videos. So your run would most likely be invalid, unless if you are running AA.

Darn yeah it was a RSG

Well you can continue later but you’ll have to keep the game running and therefor lose a bunch of time