As noted in the ToS, which YOU LIKELY SKIMMED OVER AND AGREED TO PRIOR TO MAKING ANY PURCHASES, effectively states "ALL SALES FINAL (NO REFUNDS)."
Once you buy a game from the Wii Shop, your points are spent & the DRM keys are added to your Wii Shop account. This allows you to re-download the games as many times as needed (or until you delete the Wii Shop account information) OR for at least 12 months from the date the game was delisted from the shop. If you choose to upgrade to a Wii U, you'll be able to transfer everything from your Wii (including the Wii Shop account data) through the Wii-to-Wii U transfer tool.
If you choose to delete your Wii Shop account data (which can only be deleted from the Wii Shop itself, as it's protected from factory resets), you will LOSE ALL ACCESS to the games purchased. Since Nintendo did not link shop purchases to users (like they did with the 2/3DS, Wii U & Switch with your Nintendo Network ID), you cannot transfer these purchases to another Wii (only to a Wii U, as mentioned above). If you choose to sell your Wii OR your Wii becomes inoperable, you lose your digital library. HOWEVER, in the case of your Wii breaking down, you can send it to Nintendo for repair / replacement (at Nintendo's discretion; repair fees apply). In the case they send a replacement system, they will transfer the Wii Shop Account at their repair center.
This is just a simple case of bothering to read all that fine print regarding a shop service & common sense.