Hello,
Please find my replies as below:
1) Was your site ranking on top 3 pages just prior to migration or weeks before migration? This you need to make out. If it was down much before migration, this issue has nothing to do with migration.
2) Also even some top performing sites will be temporarily shut down due to server hangups or even in case of regular temporary maintenance schedules. Search Engines don't penalize them for any temporary shutdown. This can also happen in case of sudden software crash or a major hack on the site sometimes. So what I mean to say is that your migration shouldn't be an issue at all if you say just for 2 days!
3) Now the point of indexed or deindexed: Your site is already indexed since you only said it's showing up on page 7 or so instead of top of the pages. If you use the term 'Deindexed' it may mean penalized or banned by Search Engines or you might have used robots to stop engines crawling your site. So let's not get into that 'Deindexed' and it doesn't apply to your case at all!
4) Now coming to alternative outcomes, something else: This technically if you check your cached copy of your site from the particular search engine you're talking about, it will give an idea when was it last crawled before. If it was before migration, cool! Else if it did happened during the shut down, the Search Engines have algorithm to track such temporary shut downs and may retry accessing your site. But for now you should find out the cached copied dated by just clicking on 'Cached' on your site search engine results.
5) This is a SEO question in general and may not be relevant to jobberbase site seo.
But still i like to reply to your questions as they're very interesting. Hope you got some clarification.
Thanks
www.SEOFastGuide.com