What you would do before the river is irrelevant since the question is about the river, so you should maybe instead try to understand what has happened up to here and what the Hero was thinking.
Notes before I explain my opinion:
-I will consider his range as being 40% of the starting hands, since he is in MP. If he was in UTG/CO/BU, this would have to be adjusted. This is the approximative range I will be putting him on:

-Given our info so far, he must be tagged as a maniac and handled as such, that's as clear as daylight. That's why I consider that the line chosen by the hero is one of the best, if not the best, possible options.
-Hero is in position and therefore can control the pot much easier.
-The villain is likely to double/triple barrel with almost all, if not absolutely all pocket cards from his starting range on this dangerous turn.
* It's pretty clear until the river, the hero is letting the maniacal overbetting fish bury himself, having the best hand well over 80% of the time at the very least with the top pair and considering his range,with room for improvement to a straight,2 pairs or 3 of a kind. Some of you might think that getting a second pair is a problem because any 5 in his hand gives him a straight,but given his 40% raising range, the only pocket cards including a 5 would be 55, 54s, A5s/o, K5s, maybe sometimes 53s, which would add up to 2.9% of all possible hands and a very,very small fraction of his 40% starting hands.
* When the turn comes,we're still ahead roughly 70% of the time. We can calculate this by crossing the hands that beat us with the hands that beat us and he might have. The hands that beat us are: any ten,any pocket pair higher than or equal to 77(77 being very unlikely since two of them are already out), the 2 possible straights made with 53 or 89 and any set. Crossing this with his likely range, we get 12.4% of all starting hands: 66+,44,ATs,KTs,QTs,JTs,T8s+,98s,53s,ATo,KTo,QTo,JTo,T8o+, which is about 30% of his starting range, and so, like I mentioned earlier, we're still up about 70% of the time.
* Then there's also the unlikely event that he rivers a flush,straight or 2 pairs/trips on the river, which I wouldn't worry much about even if there are 2 flush draws on the table,since he can only have one of them after all and it's a ~1/5 probability he completes it, if he actually has one. Against a better player on this turn we might either fold or raise for protection, depending on the info we have on him, but this is not a better player. This is a "macho".
* To finally answer the river question, given our pot odds and the small percentage of hands that actually beat us, I think the best play here would be calling his likely river shove or any bet, absolutely regardless of the river card, since we can't realistically narrow his range down more.
* If checked to us without us improving our hand, we should check because we will not be called down with a weaker hand, unless the opponent is on tilt or brain damaged, which is rarely the case at these stakes. If we try a small bet, the opponent might read this as weakness and go all-in, leaving us in an unpleasant spot, especially on a bad river, so I wouldn't recommend it.
* If we improve to a straight or 3 of a kind(
except if it completes one of the flushes), I'd go for a small bluff-inducing bet, since a shove will rarely be called and this opponent is more likely to shove than others. If we get 2 pairs I'd just check, given that the turn has brought us another possible straight if an 8 were to come on the river and either a 5 or a 9 would give him a straight.
* If the river improves our hand but also completes a flush and it gets checked to us, I'd probably just check for safety. We already got a lot out of him if we're ahead and if we're not, we might as well avoid losing more.
* See you in December!
EDIT 1: added "*" signs at the beginning of paragraphs so it's easier to read the post.
EDIT 2: stated I added "*" signs so that people won't worry I stole their ideas after i posted