Must have fallen through the cracks. I'm not sure what to tell you. It's very possible to patch a pool so it's permanent, but it's never pretty. How large is the slit? Last time I replaced my liner, I kept a large amount of the clean vinyl for repairs. With Boxer glue, properly applied, I've been able to create permanent repairs. If you've got a 6" hole you can probably fix it. If it's a 2' long slice, I have NO idea if it can be successfully repaired.

I strongly suggest you don't try to put on a winter cover in a 15mph wind again.