As a default are we calling river or folding?

Guess everything is pretty standard on earlier streets and playing BetFold on the turn is fine as well.

I folded because such a large part of his range contains KQ but maybe he can bluff his missed diamonds?

888 Poker - $0.10 PL Hi (6 max) - Omaha Hi - 6 players
Hand converted by PokerTracker 4

Hero (UTG): 107.1 BB
MP: 151.4 BB (VPIP: 66.67, PFR: 44.44, 3Bet Preflop: 0.00, Hands: 10)
CO: 84.8 BB (VPIP: 29.41, PFR: 11.76, 3Bet Preflop: 0.00, Hands: 17)
BTN: 173.3 BB (VPIP: 28.18, PFR: 21.55, 3Bet Preflop: 7.27, Hands: 182)
SB: 96.1 BB (VPIP: 30.00, PFR: 10.00, 3Bet Preflop: 0.00, Hands: 10)
BB: 60 BB (VPIP: 40.68, PFR: 27.12, 3Bet Preflop: 5.00, Hands: 60)

SB posts SB 0.5 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 8 9 7 T

Hero raises to 2.8 BB, fold, fold, BTN calls 2.8 BB, fold, fold

Flop: (7.1 BB, 2 players) 7 J T
Hero bets 5.3 BB, BTN calls 5.3 BB

Turn: (17.7 BB, 2 players) 8
Hero bets 13.2 BB, BTN calls 13.2 BB

River: (44.1 BB, 2 players) A
Hero checks, BTN bets 33 BB, Hero?

Villain's preflop stats look reasonably solid.

If he's thinking enough to bluff the river with a missed draw, he's also less likely to be calling the turn with just a flush draw, which puts more straight draws, sets, two pair, etc. in his range and some of those check back for a showdown.

I'd call with Q9xx and fold the rest.