I really doubt it's necessary to re-introduce them at the extremely slow rate that's recommended for first-time veggie eaters, but I wouldn't dive right back in, either.
I know keeping enough veggies in stock to give two rabbits their 2+ cups each a day every day is a lot to ask of someone... but could you ask him to at least get a little something if he's at the store for himself anyway? If he goes to the store about once a week and could pick up just a head of non-iceberg lettuce and a bundle of cilantro (which are both very cheap options compared to the herbs and watercress) and feed those over a day or two, that should keep their systems fairly accustomed to fresh veggies. You should still gradually increase from the amount he was giving to the amount you normally do (as long as they're tolerating it well, you can do so pretty quickly (probably < 2 weeks to get back to normal)).
On a side note, it's too late for this advice now, but something that might come in handy if you have to get a long-term bunny sitter again (or even just for your own routine use) is Debbie Meyer Green Bags - I recently got some to try again (hadn't used them for at least a couple years) and really love them. Assuming there's enough room in the fridge, I can buy up to a week's worth of veggies at once and they'll stay appropriately fresh and crisp in the green bags. Granted, the fridge space is kind of the big catch there, heh. We're spoiled - I bought a cheap side-by-side fridge off of Craigslist from someone who only lived 1/2 a mile away to use as a second fridge in our apartment. Between all the soda my boyfriend drinks (very little of which could actually be kept in the fridge when we only had one), all the skim milk I drink, all the juice we both drink, all the veggies the bunnies eat and up to 2 months worth of frozen dinners for my four sugar gliders, I was having a hell of a time finding any room for actual food in the fridge and freezer and a good used fridge runs $100-150 - it was a no-brainer for us!
