Will bad play in one cruise line's casino put booked trips at risk?

Potentially. In general, not playing on a trip will affect future offers as URComped's trips are based on a rolling average of play. One bad trip can bring down the average, but it depends on the case. The more good trips you have, the less impact one bad trip will have. If a player doesn't play on a trip that has already been comped, it may cause concern for the casino and they may reevaluate future comps.

There is no hard and fast policy on this, but not playing on a trip that has been comped for play could definitely affect future URComped offers.