No, you don't lose the SBD or Steemit in your wallet if you don't claim them. The money is already in your wallet, and since you alone have the key to it (unless you decide to share it with others), it will be there for as long as you want.

I have seen a few inactive steemit accounts with some SBD or Steemit in their account. The money is left there until they decide to claim it.