Yes you assume correctly. Your wallet will never "delete bitcoins" (i.e, delete your password that gives you access to the bitcoins) unless you explicitly tell it to. Still, its generally a good idea to take a backup of your wallet once you finish importing your key.

There is 0.04240537 BTC in the address you provided, or about $28 worth. So long as you have the private key for that address, your Bitcoins are safe, so don't worry about that.

Here are some reasons why your BTC wouldn't be showing up in your wallet:

(1) You haven't finished synching with the blockchain. Are you using the Bitcoin-QT client? If so, does it say "synching" when you open it (and display a box saying X days/weeks remaining on the bottom of the window)?

(2) You haven't imported the private key correctly. Just try again.

(3) You need to -rescan the block chain (this is the process where your Bitcoin client re-checks for transactions to your address).