I think that making the game online only will have the same issues as any online only games have.
Upon launch every online-only game has broken, from WoW to SWTOR and Diablo 3. Ultimately SimCity is the greatest flagship of always online DRM failing catastrophically, it is simply a math that can only make sense when explained by a bunch of beancounters in a meeting room but it is, in the end, flawed. The solely expense on authentication servers (clusters, racks, network, bandwidth, redundancy, etc...) to hold millions of registering users at the same time can be the same value of estimated loss by piracy. The investment required to do a launch "right" where no one has to wait is prohibitive as the servers will hold way more load than they will usually have after the first week. So making a huge investment for day one to have it idle on the rest of the days isn't financially smart. And in the end we have hundreds of thousands of customers looking at queues and counters when the game launches.
It is a big balancing problem, does the company invest millions on a system to help them increase their profit by another millions? Will that math even go into the black? If you invest N thousands/millions to save you from potentially losing N thousands/millions don't you, in fact, made no money? That decision will have them lose customers that don't want to play a single player game online all the time. While others will want to play it for decades and if the authentication server goes offline they'll be losing their dear game... And at that point does your purchase becomes a rental? Should you pay less for a game that is only available to you when the company decides it will be? Where do the rights of the consumer go over a decision to limit the use of the game they acquired legally in an attempt to avoid piracy?
I don't think that paying consumers should have their experience hindered in any way due to a tactic to restrict piracy. As most people said: piracy will happen anyway. So instead of restricting the legitimate user's experience, why not go the other way around? Instead of always-on, do something that incentive people to purchase the game: lower prices, free patches to registered game owners, add-ons every so often... And most importantly treat your customers properly.