Transavia pilots will operate the Dennmark based a/c at least until 1st of april. What happens next depends on what Transavia can arrange on short notice.
They want to start a subdivision just like the French division with local crew, both flightdeck and cabin. The AF/KLM group have given permission to do so. However it all depends on getting an AOC and getting the required aircraft. I heard that the ex-Sterling a/c do no meet the Transavia requirements.
However with the CEO leaving the company and a MAC/Transavia merger on the horizon I guess nobody knows what's going to happen.
But if I were you I would definitely keep an eye on things because Transavia is a very fast moving company.
As far as the KLM pilots flying for us in the summer; Since the AMS fleet for next summer is two down from last year and with 16 new guys trained I don't think there will be a shortage in Amsterdam though.