Yes, I see what you mean, its hard to come up with solutions that can not be 'gamed' to achieve other ends, such as escaping an unwanted long lease.
In which case, the 'grounded until repaired' option seems to work best : the lease payments still fall due, so there is no benefit in deliberately missing mx on them if they cant fly and earn revenues. If the airline has been abandoned, then it will come home eventually, in no worse condition.
Having had planes finally returned at levels like 4% condition, you end up spending vast amounts bringing them back into service ; a single d-check doesnt cover that amount of damage :as I seem to recall, it maxes out around +60% improvement or so ; the rest has to be done as extra maints : as mentioned, if you do lease out a lot of planes, its not a killer event in itself, but it is damn annoying when it happens especially as, currently, there is nothing you can do except watch it and weep.
I personally dont mind planes coming back at around 80%, nor if it lands home the day before its d-check is due : that's all in the deal : but these nightmare ones fall so far outside the norm, one wonders how they have avoided the 'random' in-game spot-checks which always seem to catch mine the moment get an a-check missed when switching skeds... oh well... one of lifes mysteries, I suppose.