Plus they could start up using it again anytime.
Not necessarily. Three years of non-use is presumptive abandonment, and places the burden on them to show that the non-use was excusable for one of the various reasons. If there has been abandonment in fact, then simply starting again in the future does not tack onto their original period use. You can't simply not use a mark for, say, nine years out of a ten year renewal interval, re-start use "anytime" and claim to have had continuous rights in the mark.
Here, there is an additional significant fact. It would be difficult for them to argue that they maintained an intention to continue use, because the domain name in question was abandoned by them. UDRP's in which the complainant is the party that let the name go are something of a special class, which have gone either way depending on some additional facts not stated here.
One thing that would be interesting to know is how close is this registration to the next maintenance payment deadline. The OP is probably unaware of the 6 and 10 year renewal dates.
If the renewal period expires, say, next week or something like that, then it's just a matter of days before that registration ceases to exist. Simply because a mark is registered today, does not mean that it will be registered into the future indefinitely. So one important thing someone would need to know in order to render a competent opinion, among other things, would be when was the registration issued, and when was the last renewal payment made?
If the indications are that (a) they have not been using the mark, (b) they let their domain name go, and (c) the registration is close to abandonment for non-renewal, then it may simply be a short wait before the registration is likewise gone. But there simply aren't enough facts stated in the OP to know that.