Hi there! Are you using vROps vCenter plugin? If not, you can just take the vrops cluster offline, then turn VMs off and that's all.
Please consider removing vROps endpoints from vRLI, vRA, vRO, etc.
Hope it helps!
You can also run the side by side for a couple of months so you have data in the new instance if other ppl use it so it is not a hard stop of data for them.
If you have alot of you own dashboards and customization's it may be worth while upgrading to 8.2 first and then using the new export feature
Lastly you should go to 8.2 🙂