Right now if you go to a bot that was deleted, you get a page "bot not found"
https://chromium-swarm.appspot.com/bot?id=gce-precise-c4413e93-zmxl&sort_stats=total%3Adesc

On the old UI, it still shows the history, i.e. old tasks and events.
https://chromium-swarm.appspot.com/oldui/restricted/bot/gce-precise-c4413e93-zmxl

(We have a lot of "removed" bots, because Machine Provider constantly cycles bots. Then don't live longer than one day.)