It can be quite interesting watch a PSG without Mbappe in the Champions League next season. I'm saying this assuming that he will accept Al-Hilal's offer of course. If he doesn't I think it wouldn't be reasonable at all. I know that he will have a loyalty bonus if he stays for another season here. However it is just nothing beside the amount he can earn at Al-Hilal in only a year. 
Taking al hilal's offer probably the best choice for mbappe right now. He will get the money he wanted and then he will also able to leave from al hilal next year with free agent. Mbappe just need to wait for another year to make sure he will have a chance to join in real madrid at this moment. I would call that mbappe as the dumbest player if he will not try to agree to take such offer from al hilal. I expect Mbappe to take this offer and play for them for one season. After that he can still join Real Madrid side as Al-Hilal also offer a condition like that to him. In this situation PSG will need to make a big signing. Bringing Vlahovic wouldn't be enough at all. I think they should look for a bigger talent such as Osimhen.
I read in some news said that if mbappe was feeling doubt about such an offer. Mbappe may try to stay in PSG even though he must be benched for the whole of season. Vlahovic was not enough in making the attacking line to be even better. PSG gets draw against CR7's club. It's very bad result for PSG