Outlook Express has disappeared!

I've just used Thunderbird to view mail with the intent of moving to this or using on a Win7 netbook. This downloaded the latest emails and offered to "integrate", which I rejected. After sending a couple of replies I then exited to use OE only to find that this has disappeared completely from the desktop and does not appear in "Programs" - all my emails have vanished !!!
Can anyone help. This seems even more disastrous than those who have just lost all emails - any hope of recovery. I've just realised I can try "System Recover" (or whatever) - if this does not work I'll be back. Any ideas as to how this can have happened?

 

I was working on a PC with XP with A VIEW TO using Thunderbird on a Win7 netbook! ... just because I can't use OE on it!
Thankfully Sys Restore has given me back my emails and OE, but I'd like to know whether a Thunderbird bug caused the loss of OE; it seems a very dangerous and odd thing to happen. I deliberately opted out of the "Integration" option IN CASE it might have messed up my mail! Some hope!!!