What's the blog address ?
What changes are you making - eg moving from Blogger to Wordpress or vice versa ?
On your Feedburner account (check all your possible Google accouns),
on the stats of all your different Feedburner feeds, the only thing you can export
is your list of email subscribers.
Those 5k are people who are subscribed to your rss/atom feeds
with a feed aggregator of their choice.
Tracking who they are is not really even theoretically possible,
as they are not necessarily logged in to anything.
With Feedburner, you'll at least be able to see some aggregate statistics on them.
Deleting the Feedburner feed would be the last option - at which point
you should set up perma-redirect to your new feed URL
The much better option is to update the Original Feed URL.