Indeed this match was done beforeviewtopic.php?f=17&t=7328
However, I'm going to keep this match open for one critical difference; the no-flight rule.
I was (and still am) convinced that in a match where either combatant could flee, Bio would defeat Hedorah convincingly. However here, they must fight to the death. This gives Hedorah a better chance.
Now that being said, this is NOT one-sided either way. The battlefield isn't going to be kind to either kaiju either. The ruins of Tokyo probably don't have too much plant life for Biollante to create spare vines with, and all that dust from the ruined buildings that's going to be kicked up from the battle is going to dry Hedorah up some. And with no rain and fires raging here and there, he's going to run into problems.
In the end, I side with Biollante. She can regenerate. With no moisture to help him out, Hedorah can't. In order for him to use any sludge bombs, he's literally going to have to sacrifice pieces of himself to harm Biollante. And once she hits him with the acid sap, things are gonna get pretty bad pretty quick.