According to my numbers this could be a good fight depending on how strong you think 16 is. Also I've taken the liberty of adding Trunks and Vegeta to Gero's absorptions as they arrived slightly later. Without those two Gero would get one shotted. With them he has a good chance of winning.
I think Gero should win. This is three Super Saiyan level characters we’re talking about plus some extras like Gohan and the humans. Kamiccolo would’ve been enough for Imperfect Cell to reach his limit, and Piccolo + Vegeta + Goku should give way more power.