Yes, there is an internal watchdog but correct it won’t affect squirrel code. I would go for a very very long watchdog interval (10 mins+) to ensure that upgrades are not affected - resetting during an upgrade will never brick an imp (we are safe against reset and power loss in every scenario) but if you’re on a really bad internet link and there are a lot of retries during an upgrade you don’t want to get kicked.
However, cap sizes tend to get large for this, eg https://www.mouser.com/datasheet/2/256/max6746-max6753-90818.pdf would require a 120uF capacitor (a low leakage ceramic at that) for a 10 min timeout.
Plausible for you?