I've stitched two good pieces from two different wigs together before now when I've been desperate and needed to get by before my new one arrives.
But you don't have that option. I'm not sure what you can do in the meantime other than use concealer and thats not really a great choice.

If you're thinking of having it 'repaired' in the sense of getting more hair put on the shedding patch, this is a service that Debbie offers, but its time consuming.
She has details about it on her website but points out how long and how much it costs per area. She uses a coin to illustrate that area, I can't remember which coin but she makes it quite clear that after a certain size its just not cost effective and its cheaper to buy a whole new unit.

As for what you'll do with the old piece when your new one arrives, you'll have to decide.
I used to find them hard to throw away in the early days!
But soon there were piles of them and it was pointless and verging on Andy Warhol madness who kept & logged every piece he'd ever owned!
I had an amnesty and flushed a load down the toilet.
I kept the ones that were a good colour and use swatches from them to send away for colour matching.

The lesson from this is ALWAYS HAVE A SPARE!