Rashou
Weren't their suits capable of withstanding extreme heats? So long as Johnny doesn't go Nova immediately, Violet could put a field around him, or Dash could create a whirlwind to keep oxygen away from him. And Mr. Incredible could then pound him after that.
Actually, Jack Jack's suit was designed to withstand extreme heat... the other suits were all custom designed for their wearers' abilities (my Dad and I have theorized that Jack Jack's suit may have also been designed based on his abilities, and that Edna was only feigning a lack of ability to predict what his powers would manifest as, but there's no real basis to this conclusion).
There's reason to believe Ellen's suit may have some heat resistance (as well as concussion resistance), since it did a pretty good job protecting her from the full effects of the explosion that took out the plane. Dash's suit is mainly about reducing friction, although I suppose it may have had some generic heat resistance thrown in there as well. From the way Edna was talking, I got the impression Violet's suit had to sacrifice most of the standard add-ons just to be able to share her invisibility. I have no idea what Bob's suit does, as it's not explaned in detail such that I know of.
So meh. I actually have no idea how useful the suits are for that scenario.