What will happen to the old CGI webspace?

[#1]

What will happen to the old CGI webspace once the migration is complete? Will it be shut down or just not supported?
I only received the email for the new control panel this week, so I'm reluctant to change any domain DNS records until I've tested it for a while. At the moment I have a domain transferred in to Plusnet which is pointing at the old (original) CGI webspace. How long have I got before this no longer works?
Sorry if this has been answered in the FAQs, but I couldn't find it.

[#2]

Plusnet have said it will be 2-3 months before the old servers are shut down. However I don't imagine they'd be regarded as supported, so if anything major happens service from them might end sooner.
David

[#3]

David's right on the money.