My site dropped from #1 to oblivion last week, even for its own content (searched in quotes) and for its domain. This may be due to the update that occurred or to the fact that I had just changed hosts and file formats (from traditional asp to .aspx).
BUT, slurp still spiders the site (most pages) everyday. I have heard that if you are banned/penalized it will just grab robots and index.
Yahoo probably still has the original .asp pages and is only now indexing the .aspx pages, so they probably don't rank as of yet. What happens when people try to access the original .asp pages? 404? 301?
Hard to tell without more info...
Regarding a possible ban:
If only your home page is there, you've been banned regardless of the behavior of Slurp.
I've seen Slurp grab other pages every once in a while. But they never make it into the index.