Three albums and tours in their contract? They'll have to find a loophole to get out of it because there's no way they'll manage three more albums and tours given how they work. This will be their only album this decade, barring a miracle. I'd be shocked if they were more productive next decade, when they're all in their 60s, than they are now. I think it's more likely that NLOTH is their last album than we get three more albums and tours.
Of course, they could do smaller tours and be a full-time band again, but what are the odds of that happening?
The only thing they owe is promises they've already been paid for.
U2 have not been paid anything for albums they haven't made. So they actually don't owe any albums to their label, it's just IF they do make a new album, they have to release it on Universal (Interscope, Island) until those three (if that's what the contract says) are provided.
This is aside from any guarantees that pertain to music that has already been recorded (Box Sets, Best Of's). I'm talking about new music. Any artist could die tomorrow, so not only will they not be obligated to provide future releases, they won't be paid for it. And vice versa, because they aren't paid anything for it, they aren't obligated to provide it.
This is factoring in the implausibility of a 'shit deal'...some artist out there might very well have a 'shit deal' but certainly not U2. U2 will have every advantage and have all the bases covered. More on that in a moment.
The worst case scenario for U2 (should they retire tomorrow) is that they'd owe money to Live Nation. And we don't know if they received advance money for their Live Nation deal or not. Based on the reporting, it sounds like they may have. As all the reports say it's a similar deal to Madonna's LN deal.
But even so, the Live Nation deal is for a number of years (expires in 2020) and not number of albums. So, for all intents and purposes, their Live Nation deal is for one more tour. Unless someone believes they will actually squeeze in two tours in the next 6 years. Not to mention this LN deal was signed in 2008 and any advance money was likely paid PRIOR to the 360 tour. So who is to say that, even if U2 had received advance money, that they aren't totally square by now? Especially after the biggest selling tour of all time.
And finally, as I alluded to previously, knowing Paul McG's crafty ass and U2's general business savvy, they surely have all bases covered. I wouldn't be surprised if Universal is actually on the hook for that money. In other words, I wouldn't be surprised if U2 didn't owe a future cent to anyone for anything.
Regardless, almost certainly U2 will tour again at some point before 2020. But there is nothing in the world beyond their own personal desires that says they have to make another new album, much less three.