It's too early. There are a couple in house options. But honestly, it's a position pretty readily filled in the draft.
Seattle won't have the cap space to spend 5M on a replacement OG. So it'll have to be on the extremely cheap. Consider there are 19 players they will have to sign to fill their 53 for next year. With considerably less than 18M in cap space to do it. The current cap for 2019 is at 19.2M, but expected cap (actual minus draft pick salaries and reserve for IR for the year), is probably closer to 12M.
So that's 12M split 19 different ways. Until we start talking cuts. Of which there are very few candidates that I've touched on elsewhere. Players that are going to hurt to let go (Wagner, Lockett, Brown, Adams or Dunlap).
Reality is, we're going to be dumpster diving for almost half our roster next season. With 3 draft picks (Zero comp picks and no first rounder), we're not getting help there either. It'll be vet minimums for a LOT of roster spots. Fortunately, there should be some better quality vet minimum players with the way this market is going to shape up.
We are currently not going to be able to reap benefit of what is going to be a once in maybe our lifetimes depressed market. Realistically, there are about 10 teams that are going to get a mint of one year rentals of superstars at 4-5M contracts apiece. And then clean up on the comp pick reimbursement in 2022. The market will be glutted with cap casualties.