Saved yeast slurry - what should I do with it?

I brewed a batch of Schwarzbier in late December using Wyeast 2206, and I saved the slurry with the intent of brewing another lager soon after. This didn't happen and the slurry has been sitting in a kilner jar in the fridge... How long will the slurry last in the fridge? If it's still ok to use, would I need a starter or would it be ok to toss it into another batch?

I didn't wash it or anything - just decanted it into a sterilised kilner jar.

Make a starter to make sure it's live (should be!) and if it smells good then pitch it.

I do this as a standard proceedure. I brew a LOT, so I just pour my slurry from the fermenter into a sanitized Ball jar and cap it off. I usually use it again within a month or two at most, but have gone as long as 6 months with good results. (I did have to do step starters and decant/wash with the 6 month one, though.)

Dump it and buy new yeast.

that old, dump it.

If everything was properly sterilized then the yeast slurry should still be fine.

Did you rinse or just scoop up the slurry?

If rinsed, I'd make a starter and go. If not, I would be inclined to dump it. I don't have experience to back up this advice, but I try to be conservative about things like this---when in doubt, I'd rather spend $5-$15 up front on fresh yeast (and starters, etc, if needed) than risk losing a batch.

In any case, with near certainty it will make beer, but the yeast is not likely in great health. The current standard advice from the published experts is that rinsed slurry should be used within a couple weeks and, IIRC, that slurry should be reused faster than that. Based on this forum, many, many people have success reviving rinsed slurry after ~months to a year or so, so I feel pretty confident about that. People do clearly get results they're happy with reusing the slurry, though, so you'll just have to gather the advice and information and decide what you're comfortable with. Good luck!