Based on observation of selecting flap at 19,000, above 20,000 with flaps 1 at flaps 1 speed, I reckon you will probably be at or in or very close to the lower amber band. Not the end of the world, but clearly not in normal territory.
Interesting how the limitation is actually worded as "max flap
extension altitude" (i.e. selecting flap), inferring that climbing past 20,000 with the flaps already extended is not included in the limitation. Bad wording or deliberate?
Surely if your departure field is unavailable after departure, you should have a takeoff alternate already?
For a short sector, your destination maybe your takeoff alternate. With the flaps not retracting you may or may not have range to make a suitable field. Makes for a good scenario for assessing how well the crew balance the relative risks. Arguably makes for negative training if the best solution is to bust limitations and minima.