Both guys are under contract for next year, and will be restricted FAs the following summer, so nothing is imminent. If OKC wants to play with the big boys, they'll have to pay with the big boys. KD, Westy and Perk will make around $44m combined then.
Give both of them back loaded deals starting at $10m per year before they hit the market, and the Thunder will have $64m wrapped up in their five best players - not unusual for contending teams, but a little high for a small market one. OKC is a small market, but ownership has relatively deep pockets.
If ownership doesn't want to pay, Perk's the logical guy to go in two seasons. If Harden and Ibaka both want to get paid more than $10m at the beginning of the new deal, OKC will have to make moves.
I'll take wither one of them on the Cs in two seasons, and both will probably be worth max money to a team without two superstars in front of them. If DeAndre Jordan can get $10m+ per, Ibaka is worth at least as much. Manu is a good comp for Harden and he's an $11m player.
I think OKC retains them both.