Jovica
Height-keeping requirement is ±200ft from the FL, so if you lose 2500ft in few seconds you do not meet the requirement. Or you do?
While I am not in a position to comment specifically on this case, if they indeed lost 2500ft in 'a few seconds', that would equate to a rate of descent well over 10000fpm. As a pilot I would be much more concerned initially with that than with telling ATC what was happening. Once controlled flight had been resumed, ATC would be right up there at the top of my list.