After brewing ales for 3 years, 1+ all grain, I got decked out with a fridge and some temp control, and tackled my first lager on New Year's Eve. In order to support my LHBS, I bought a vial of WLP830 that was about 8 months out of date. To compensate, I tried making two one liter starters with a stir plate to get to my target pitch rate. After 2.5 weeks, bubbling slowed way down and krausen was mostly subsided, so I began to cold condition without taking the gravity. Extremely dumb mistake. After 2 weeks cold lagering at 31F, I finally checked the gravity. In that 2.5 weeks of fermentation, the beer only dropped from 1.053 to 1.046. Woops.
So I got a fresh vial of 830 and made a starter. I plan on raising the temp of the beer to 50-52 or so, pitching the yeast starter at high krausen, and seeing what happens.
Questions: Is there any risk of nasty stuff like botulism from letting the wort sit so long with only minimal alcohol?
Should I keep the existing yeast cake in play? Make a starter from it and pitch that later? Toss it?
Should I reoxygenate the beer before pitching the new yeast?
Any ideas or stories of similar experiences are much appreciated.