if you do ditch the tank, though, you can expect that if you're growing them in the same location indoors, the dew will still evaporate from the leaves even faster (unless you give them more light).
Where I grow mine (on the tray method), the air is pretty much stagnant, so they always have dew on the leaves even when it gets to 85F-90F under the lights during the summer (I have a separate grow area for my cool-loving sundews like pygmies and South American species). But the sundews growing in the warmer conditions are only ~2-3 inches from my T-8 fixtures, so most of them are completely red and have maximal dew production, it seems.
Not having dew during the warmest part of the day isn't necessarily a bad thing unless the plants look like they're declining. If they were growing outdoors and this happened, they obviously wouldn't be able to catch any prey during this time, though.