Mourinho would undoubtedly have been my 1st choice last summer, and he probably represents the closest you can get to a 'sure thing' in football. Guardiola and Klopp are also brilliant of course, but there is absolutely no prospect of any of the 3 leaving in the short term.
Rudi Garcia is currently doing a fantastic job at Roma, having previously managed a very attractive Lille side, but he's only been in the job for 7 months, and with the team looking like certainties for a top 3 finish, he will surely want to take them into the Champions League next season. Conte and Simeone are also doing very good jobs at their respective clubs, but they have each only served 2 full seasons at this level of management, and might still represent something of a risk. I’m not sure either would have much interest in leaving either.
Van Gaal seems to be mentioned a lot as a potential candidate, but like Mourinho he has a reputation for belligerence, and his last big job at Bayern ended in a premature sacking, with the club struggling to secure Champions League qualification, and the manager having reportedly lost the dressingroom. Despite having done a good job so far, a few Oranje fan friends of mine are looking forward to the hastening of his exit from the national team set-up, citing van Gaal's unbearable arrogance as a contributing factor.
Solskjaer and Laudrup would be poor appointments in my view.
If things don’t improve, particularly after Moyes has been given what will presumably be substantial backing in this summer’s transfer market, he would obviously have to go. If anything though, the relative paucity of alternative options available right now, only lends further weight to the general view that Moyes probably has at last 12-18 months to rectify the current problems before his job comes under serious threat.