+1 to the above. Warm it up and let it burn out/clean up the diacetyl. You don't have to keg it once fermentation is complete. Lager it on the cake for a few weeks if you can. It will continue to condition and the yeast will go to sleep with nice reserves so you can reuse them on your next batch.
that's the game plan. plan on moving it back to 55F, then drop it a few degrees each day until 45F and leave it on cake for 2 weeks. then i will rack to keg for another 3 weeks at 34F.
Why stop at 45F on the cake?
For me it is always just an issue of space. One month in primary then to keg for bulk aging at colder temperatures - the kegs fit easier into the fridge that serves as my "on deck" area...and I need the space in the lager chest for the next batch going into primary.