They can easily halt the software upgrades whenever they want.
Sure, but do you think that it would be a smart business decision to tell their clients: you know what, all those Nano S's you bought, are now useless? From tomorrow, you wont be able to connect to Ledger Live. Hahah, suckers.
Also, something you both didn't say (or I've missed) : it also depends on how other software will behave. I mean that unless something fundamental changes or some big flaw is found, I don't see why Electrum wouldn't support the Nano S for many more years after Ledger stops updating it.
Good point. But there is still the issue of not being able to update your Bitcoin crypto app or install the newest firmware. In case your Ledger resets itself, you wont be able to configure it without accessing Ledger Live and downloading the BTC app as well. But yeah, Electrum should still work.