Junior Siavii and Kentwan Balmer are potential in-house replacements for Red Bryant at end. Seattle should be able to find someone that can approximate Bryant's contributions as a run stuffer.
Red Bryant was probably the Seahawks best defensive linemen through seven game. With him out, the Seahawks run defense weakened significantly against the Raiders. I'll say this, and it might prove untrue, but I don't think it is: Seattle's run defense can weather the loss of Bryant.
I think this because before Bryant started as Dan Quinn's supersized end, there was Cory Redding. Both players were converted defensive tackles that sort of straddled definitions. Redding and Bryant exist somewhere between a 3-4 end and a 4-3 tackle. The implicit sacrifice of starting an end at tackle is the loss of pass rush, and even though Bryant performed a bit better than expected, he was mostly a component pass rusher. Bryant set the edge so that linebackers and defensive backs could rush.
Now that Bryant is on injured reserve, we get to see if Bryant was particularly capable of stuffing the strong side or if another tackle-end type can also jam offensive guards and tackles. Frank Okam seems like the obvious replacement. He is huge and long-limbed, but plays upright for a tackle and loses leverage. So, Red Bryant. He's not as quick as Bryant, but I'm not sure we'll see that difference. Seattle signed Okam to a two-year contract. That means he is coming in to play, and given his tools and skills, I assume it means he is coming in to take over for Bryant.
The blitz might suffer, but I doubt the run defense will suffer too terribly much.
It's interesting, because though I think Bryant was playing at a higher level than Mebane, I don't think Bryant is nearly as irreplaceable as Brandon Mebane. Under tackles that can penetrate and stuff are pretty uncommon, and though Kentwan Balmer hasn't played poorly, I don't think he's Mebane's match. Maybe I'll regret assuming Okam can approximate Bryant's contributions, but I doubt it. If you're willing to forfeit pass rush from part of the front four, it's not terribly hard to find someone that can stuff the run.
Now, will Seattle's strong side pressure still work? That I am not sure about.