SVB was the 15th largest bank in the US. That's not a small bank.
The account holders' accounts, and likely all the loan portfolio, will go to another bank. The new bank will adjust its reserves from the Fed in the usual way, and may get some capital from the FDIC (warning: I am not au courant how the latter works post the GFC).
The FDIC uses its own large (and augmentable by congress, not that it matters in this case) balance sheet to back some or all of the deposits. It seizes all of SVB's assets and unwinds them as it decides to...with the proceeds going to FDIC.. Whether it dumps them on the market or holds to maturity is the FDIC's decision and has nothing to do with what happens to SVB. The people who went to SVB HQ and the people who decide what to do with SVB's assets are completely different people.
Read my reply to kmod.
> SVB was the 15th largest bank in the US. That's not a small bank.
The money center banks are the ones that matter. Most retail deposits are held by a handful of banks. Being the 15th largest bank is not like being the 15th university in the rankings (i.e. not that different from the top 10) but more like being the 15th biggest car company. I wouldn't call FDIC's balance sheet "enormous" but it can handle SVB without breaking a sweat.