Should I be concerned about overheating when doing long render tasks?
First answer to "My question is if this heavy workload will decrease the life of my computer."

Simply YES, 
BUT any  work on a computer will decrease its life, but it does depend on the work being done and how intense it is, but on the other hand, computers are designed to work in different ways and workloads. Desktop Workstations like the HPs and Mac Pros are designed to run massive tasks and just chug away at the data, which is why you will see the pros using them in the big studios as they power they offer is fantastic. They can have 12 cores, tons of Ram, brilliant GPUs etc which a tablet cannot.

Now you can still get high powered desktops from the likes of home builds and retailers which will handle data happily and run all the time.

Tablets (including the Surface) are really designed to be a portable solution that is not a laptop and even though they have loads of power and do the job they are not really designed to sit and chug away at data for hours on end as the little fans and main boards are so close together and the heat that is generated can affect the components over time.

If it was me in this situation I would do my work on the Surface but I would have a desktop (HP, Mac Pro, home-build, etc) to send the work to render on over night and or all day and having the ability to upgrade or add in new GPU's more Ram multiple processors/cores will cut down render times about also increase your work as you can render on the desktop and still produce more work on the tablet.

Other option is sending the files to something like and online render farm to render them out and send back the finished product but this is a bit of a more expensive option specially if it is just smaller project and not rendering films like Pixar's Cars or Disney's Moana.

Obviously this all involves spending more money and have extra kit but it might prolong the life of the tablet and cut down render times etc.

Now this is all great in saying this but putting things into practice can take a long time to work out a good flow, I'm still improving my flows daily while I'm working.