Not that I love the Glazers, but their clutch of the purse strings has not been the issue over the course of the last 3 summers in which we have dipped a fair bit into the transfer windows. We haven't matched Chelsea, City, PSG, Barca, Real or Bayern in terms of fees, but we have spent on Kagawa (16m), Young (18m), Jones (19m), De Gea (18m), Zaha (15m), Van Persie (30m), Fellaini (27m), Mata (37m) and other smaller fees for Powell, Buttner, Henriquez (any updates?) and Guillermo Varela. That's upwards of 180m in transfer fees since the 2011 summer transfer window. Even accounting for player sales we have spent upwards of 150m in that time.
I actually think we'll see them continue this type of spending with perhaps a 100m window either this summer or next with the lucrative TV deals and revenue sharing that are now part of the collective bargaining agreement in the NFL along with the strict salary cap make their ownership of the Tampa Bay Bucaneers a risk-free investment in terms of operations costs and salary and one in which they turn a nice profit annually. In combination with the sponsorships United has in place and the lucrative new PL TV contracts 50-60m spent per window is a reasonable expectation, even if we are with CL football for a year or two.
From looking at how they've dealt with coaches in the NFL they will want and need to see improvement from the manager and in results next season. If we finish in 5th, but are trending up through the season I think Moyes will have earned a 3rd year in their view. If we are abysmal and look much the same as this season throughout next year's campaign they are highly likely to make a change. If Moyes makes it to a 3rd season then he'll absolutely need to clinch a CL spot and challenge for a title. If that is accomplished a sustained title push would be the minimum expectation every year following that.