I've been on a LOS since v18 on a Samsung device, and — barring a handful of inconveniences — I love it. (Most) things just work and I'm confident they will keep on working for a good while. Hardware will probably fail earlier than it losing software and update support.

That being said, I dread having to bump major versions on LOS, but I'm not sure if there's any getting around it. When I upgraded from v18 to v19, it was a massive chore to backup and restore what I had since the upgrade required a full flash, and that meant all data on my device is goong to be wiped. Now there's an outstanding upgrade to v20 available for my device, and the only reason I've been putting it off is the data wipe and restore tedium.