The only widely distroed brands that regularly send stuff I want to buy to GR that I would be upset to see pull out of our market would be the Bruery and Dogfish Head. I'd add Cascade to the list, but I get the distinct impression that they sent a huge shipment of standard stuff a while back and washed their hands of MI, since I never see any of their relatively newer creations that I'd happily spend the money to try, and that other markets seem to get. But when I think about other big brands (Sierra Nevada, Rogue, New Belgium, Anchor, Stone, Ballast Point), and I can honestly say that their disappearance would minimally impact my purchasing habits and satisfaction.
I happen to buy a fair amount of local craft because that takes up so much shelf space and is most conducive to my inclination to tick, but I'd be perfectly happy to spend 100% of my beer budget on non-local beer assuming favorable distribution conditions. The problem is that non-local breweries tend to ship too sporadically, they often send stuff that is already old (Alesmith introduced themselves to MI last month with a pale ale that was close to 3 months old at launch if memory serves), and there is often a premium that is hard to justify compared to the local stuff (Almanac being especially brutal). And so between those negatives and the internal distribution of Michigan breweries (Transient and Ellison especially) improving a great deal, I feel like I'm being forced into buying local without being terribly enthusiastic about it, since my favorite breweries aren't local.