Possible Dead Yeast Starter?

I am hoping to brew tomorrow morning and am worried that my yeast starter is not active. I need some last minute help, if possible.

I made a 1L starter 2 days ago and bumped it up to 2L yesterday. The vial of WLP-570 yeast was about 1 month past expiration and was in the fridge for several months. Additionally, when it originally arrived in the mail, it was an extremely hot day and the yeast vial was quite hot when I pulled it out of the box .

Since I didn't trust the yeast, I decided to take a gravity reading today to see if my starter has been fermenting at all, and the reading is very high (1.048) . The starter also tastes sweet, like unfermented wort. Ignoring the fact that I probably put too much DME in the starter to begin with (the gravity should probably be lower even as a starting gravity).... I assume this implies that the yeast has not even begun to ferment the starter.

Can I pitch this yeast?

Or should I substitute with some Nottingham that I have on hand? This would make my Belgian IPA just an... IPA.

Thanks so much!

You don't indicate what your starting gravity was, or how much DME you used to make it. But, like you, I'm not confident that the starter is good. Probably I'd take a shot at it anyway, but keep that Nottingham handy.