That's a different case than where you lose your hard drive with wallet.dat and have no backup or something like that.

With a hosted (shared) EWallet, the service still has the funds, just that you never access them.

InstaWallet has said that if they ever were to shut down they would make create brain wallets that used the InstaWallet address for the pass phrase and send the funds for each InstaWallet to its Brain Wallet equivalent.  So that the funds could eventually be spent.

So, if that were to happen, then yes -- those coins would likely never re-enter circulation again.