Saurreg,
I'd rather Andas didn't get to Weathertop until well into the battle. "Well into" signifying after the first group (Veryadan, Aidwain, and Osric) and possibly after the second group (Luinien, Thoronmir, and Menecar). You could even have him show up right at the end.
The point is that he'll be with them and he's trollbait if he goes back to Bree. I don't mind if he participates in the battle somewhat. But I'd like you to think it through first: Is he more likely to cut and run (like the old Andas) or to jump in the fray with both feet (like the new Andas)? Will the sight of violent death and in-progress battle cause the new Andas to revert to the old? Will it have the opposite effect?
Just to jump-start your thinking. Let me know what you decide, or pose a specific question and I'll discuss it some more. Carry on!
Nuranar