I don't think this sale indicates a lack of ambition, that we held out for an inflated (let's be honest) price I think it's an indication that we are not a selling club.
That players want to move to higher paying clubs, that may be seen as more likely to win things is just a realistic impression of where we are as a club, we have to prove we are better before anyone will believe we are better, and if we can restrict our sales to one key player per season, for more than they are worth then we are doing well IMO.
Also Signings like Tielemans will only be possible if they feel they won't be held back if they do well.
I am led to believe that a deal was already agreed for Dunk a little while ago if Maguire were to leave, so that should be sorted quickly. He doesn't strike me as the best option, but as with Maguire he may improve drastically coming into a better team.
Maguire will be missed, but I don't think his sale alters our ambitions.