Preface: I'm not a trained sysadmin. Just trying to learn as I go. Please be gentle. :)
Background: So we rented a VPS to act as our domain controller. Joined ~500 of our laptops to it. GPOs were working perfectly (thanks to advice from grawity and others on my previous question). But the VPS was very unstable, kept restarting around every 10 mins for reasons I couldn't figure out. In the end I installed 2012R2 on the VPS instead of 2016, promoted it to domain controller again and reconfigured the GPOs. I also set up another VPS as domain controller to act as a sort of backup. The servers are stable and everything works.
Problem: After I reinstalled OS on the DC I can't see the ~500 laptops that were joined earlier among the list of computers. I checked 1 laptop and it still shows itself as a member of the domain and still has existing policies but "gpupdate /force" fails and I suspect that all the older laptops won't be receiving any further updates on GPOs. At this point I don't mind manually rejoining the computers but almost all of those laptops are in the field. So I could either ask for a recall which is not gonna make me any friends or send them a .vbs script to join the computer to domain again and ask them to run it which, even if I assume everyone does, the .vbs contains the root password to the domain controller so that's a non-starter. So here's my 2 questions:
Is there any way I could rejoin those old laptops? Given that the laptops still 'consider' themselves as members of the domain. I think if I can just get them to show up in the domain computers list, I could reset the computer account and the trust issue should be solved... I think.
We're unsatisfied with the support from the VPS provider and want to switch. Is there any way we can move to a new VPS with a new IP and not have to rejoin the computers again.
(I suspect the answer to second question would also answer the first one by default but I don't know for sure, so leaving it upto you.)
Bit of relevant info: We're using a publicly routable .net domain registered on godaddy. Using custom nameservers (ns1..net and ns2..net both pointing to the IP of dc1 as of now). Since the domain is publicly routable, we have set DNS of computers to 8.8.8.8 & 8.8.4.4 instead of the DCs ("gpupdate" works on newer computers with this configuration).
Thanks for reading and appreciate any guidance you can provide.
EDIT: System seems to have marked this question as duplicate of "Command to remove computer from non-existant domain". Completely different question though