No it’s really not. We’ve been left SOL on numerous occasions and the churn rate is so high that it’s literally only safe to use the bits right at the middle of their products. And we’re talking on a relatively short three year window here.
Silverlight was unfortunate but overall good for the web. You must realize that even Flash, the vastly larger competitor, also died and gave way to much better browser native APIs.
I don’t know about Windows workflow but it’s important to keep in mind the difference between abandoned products vs the changing software trends landscape.