I don't have a strong opinion one way or another with respect to handling activity, though I know that SE doesn't generally revoke moderator status unless truly absent and they can't reach you. That's happened for this site before, leading to me joining the moderator group.
However, on the subject of heavy lifting, it's not something I'm super worried about, I visit many times a day. The only issues that I can think of, off the top of my head, with this are:
I seldom have much time to answer questions now. Many require a real effort and the moderation tasks can take away from the time I have to otherwise give which, to be fair, is added to by my being a moderator on another site as well. I'm not terribly fussed about it, good answers are happening regardless, but I once had a much stronger reputation growth curve here and reputation score is part of the gamification after all. :)
The moderation culture of the site is now effectively dictated by me. This could be good or bad, depending on your point of view, but it's still based on my views almost exclusively. While I feel confident that I've generally been true to the essential desires of the community, there are likely exceptions and I'm sure some feelings/egos have been bruised as a result. Not really desired on my part, but I'll never please everyone as a referee.
I've been terrible at keeping the contest rolling properly... It's mostly because I don't really think about it and there isn't a notification trigger on the site for it. That is a consequence of the question not being mine, so it would be handy if there was a means for a moderator to "watch" a question and get notified of answers and changes. Hmm... may look at proposing that feature.
In any event, I haven't called for help because I'm not really overworked on the site (and Jon does pop in reasonably often), but for the reasons above, it may be desirable for the community to consider requesting some changes or additions.