While ADV isn't around per se, they do still exist as all those smaller companies split up like Seraphim, Section 23, Sentai Filmworks, etc. As Adam Sheehan from Funimation put it, "ADV isn't out of business. ADV did remaster itself, as you might call it, and change itself into multiple different companies (Section 23, etc.), holding different parts of its brands, of its marketing, so [it's] still around...the best way I would describe it is to think of it as Voltron. if it turned back into the five lions, so its not the one Voltron robot anymore, so the ADV logo is no longer around, but the lions and all the properties are still around."
To my knowledge, part of their downfall came from over-extending themselves with manga licenses in the years leading up to the dissolution of ADV. They got hit hard when the manga bubble burst, like Central Park Media, Tokyopop, etc. On the anime side, they did have a few shows that showed regularly on TV like Monster Rancher and Rurouni Kenshin, but none that had seriously long runs. I'm not sure that Sgt. Frog would have "saved" them anyway with the severe contraction that occurred in the market, not that their current situation is terrible, either.