Given the current travel restrictions situation, do you think it is still wise to convert my expiring UOB UNI$ into miles or get the cash rebates @ 8700UNI$ for $100?

Krisflyer miles are valid for 3 years. If you think that travel will not be possible in the next 3 years, go for the cash rebate. You should also be aware that SIA has been extending validity of expiring miles during this period of travel restrictions.

I own the PRVI Miles Credit Card and have already use the UNI$8700 to offset $100 from my credit bills because travelling overseas is still a long way to go given the current situation and even if I can travel, I wouldn't do it now until this pandemic worldwide is cooling down. So, I feel its better to convert now to rebates than to hold it and then UOB will revise its rewards again causing less value to the points you have now.