When flying the Lear 45, the operator I was at did not use idle descents or speed mode as they caused both a very high rate of descent and an uncomfortable hunting in pitch to capture the target speed.
We tended to use VS mode and 2-2500fpm at an IAS assigned by ATC then use time to level off point to adjust VS to make any altitude constraints. If not given speed constraints we used 300kts and would be descending with some amount of power on. I found this an odd quirk of the aircraft when I first started flying it but quickly got used to it.
I can’t remember clearly what we used to brief for RTOs as it’s 5 years since I flew it but it was the standard Fire, Engine failure, reversed unlock or any other red warning plus Captain’s decision on the aircraft being unsafe to fly. Basically any audio callout or master warning. Having tried a reverse unlock several times in the sim I would say that is the hardest scenario and on a long runway given the aircraft’s stopping ability (easily less than 1000m) would be inclined to put it back down rather than try to fly away.