If you are moving to Webex from on-prem you can work with your partner and Cisco and they will support you during the transition. If you are moving to something other than Cisco you are most likely at the mercy of your license expiration date. You can always ask for temporary licenses but it's not guaranteed. If you go past the out of compliance grace period, your system will just be able to make calls, and nothing else. You will not get support from Cisco but a partner may help. It's all about how much risk you are willing to take on whether you pay or stay.
