Until it doesn't work anymore.
However, the regular versions of LinuxMint are supported for 18 months and the LTS versions for 3 years.
Mint-10 is a regular version > so it should be good to go, for at least, another year.
After which time it will still work, it just won't receive any new updates.
There are still people using Mint-5 and Mint-7 with success. They see no reason to change or upgrade -- yet.As long as, it's not broken ... don't fix it.