Will the UTM continue to function after EOL?

I, too, would like to know. It's a shame that good hardware, SG210 in my case, would have to be trashed as e-waste. If possible, I would love to use the hardware in a lab environment. I wouldn't need to use many of the additional features like network, email, web, webserver, and wireless protection, sandstorm, and endpoint antivirus. So long as I can route data, I'd be happy.

Would there be a license that we can apply which would disable those features, along with disabling the Up2Date functionality? Or conversely, enable all features with the specific understanding that the device is for non-production-environment use since it would be susceptible to future attacks because the patterns will not be updated?

You can always convert an SG license to an XG license.

Thank you for the option but I do not believe this is a recommended solution.

From the Sophos UTM/SG End-of-life: Frequently Asked Questions thread:

• You do have the option to install Sophos Firewall OS on your existing SG Series appliance, however, we would not recommend this at this time for the following reason: 
  • Your SG appliance then follows the lifecycle milestones for the equivalent XG model, meaning it will be EOL on March 31, 2025 

I may be misinterpreting the effects of migrating to the XG license. If I am mistaken, could you explain the process in more depth? Is there a license level that will enable basic operations in perpetuity?

Thank you for the option but I do not believe this is a recommended solution.

From the Sophos UTM/SG End-of-life: Frequently Asked Questions thread:

• You do have the option to install Sophos Firewall OS on your existing SG Series appliance, however, we would not recommend this at this time for the following reason: 
  • Your SG appliance then follows the lifecycle milestones for the equivalent XG model, meaning it will be EOL on March 31, 2025 

I may be misinterpreting the effects of migrating to the XG license. If I am mistaken, could you explain the process in more depth? Is there a license level that will enable basic operations in perpetuity?

It depends, if not sure, look here:

Sophos SG: Appliances that are eligible for an upgrade to Sophos Firewall

Link: https://support.sophos.com/support/s/article/KB-000035565?language=en_US

We have put together some information on product behavior as licenses expire and the end-of-life date passes and added it to the general FAQ here:  Sophos UTM/SG End-of-life: Frequently Asked Questions