Discussing allegations of fraud and consequences when a short-term visa holder tries to convert to green card or another long-term visa from within the US.
What happens if green card expires while away on reentry permit and it's not possible to stay and return to USA to renew?
You lose your green card status. Reapplying or trying to get a returning resident permit would be the only two options that I can think of.
Is it a problem to travel outside the US after the temp GC has expired, and assuming the I-829 wouldn't get approved by then ?
When the I-829 fees receipt is issued, it should state that your green card is extended for one year and travel and work during this time is permitted.