I don't think there is much need for England to panic - rather, it ought to be motivation for them to push harder to improve. The first test was a nightmare, but they controlled large parts of the second and third games and, but for a poor collapse, an incredible partnership and maybe less than good fortune, they were well in the series.
But it has proven a lot of things; that Morgan is not yet a Test player being the obvious one. The problem is as Buzz points out, who to replace him with. Serious contenders would seem to be Patel - we all need to face that England are desperate to have him even show the merest semblance of restraint with the knife and fork because they see a spot for him - Taylor, and possibly Root. Now, for me, Root is a long way short at this stage and is really not the type of batsman you'd want at six anyway, but he's a more than useful offie and will be an excellent player in 18 months time, so may be worth a look see.
Of course, if Ben Stokes develops, he has the six spot sewn up...