Pretty big. You say it was a pretty heads up play to fall on the ball for a safety, I disagree.
I think a safety is the worst thing that can happen, because you completely squander your first posession, and unlike a fumble return for 6, you don't get the ball back.
So they gave up points AND had to give the ball to Seattle with good field position. And since seattle kicked off in the first half, they would essentially always have at least one more possession.
You can't give a defense like that, that kind of immediate advantage and seattle's offense that kind of leeway. I think to beat Seattle, you have to put the pressure on Wilson and their inept offense, and that safety liberated them of that.