Nothing´s ever guaranteed.
Expectations from Marquez are certainly through the roof right now after his amazing performances. If he´s not like in top 5 in these first tests, I bet some will see that as a disappointment.
I think at this point he is the biggest promise to enter MotoGP since Rossi. And unless he gets badly injured (remember that eye injury he had, was career-threatening), then he will be also a MotoGP champion one day. But it might take several years.