Im not sure StL would do #2. At this point Allen, for all his gaffes, is far better than Greiss and he’s only signed for ~$1M more and 1 Season more than Greiss.
A Greiss buyout is cheaper and shorter than an Allen buyout. I can't think of a good landing spot for Allen that wouldn't necessitate similar money going back the other way, if the Blues want to start fresh.
Even if they didn't want to make the 2nd trade, the Blues still strike me as a team with the best balance of need and assets outside of the division for Washington to look to for value.