I've known several biopsy proven celiacs who had only a positive antigliadin IgG. It is absolutely possible.

According to several studies, as many as 20% of biopsy proven celiacs do not show positive anti-tTG or anti-endomysial, especially if there is only partial villous atrophy.
http://jccglutenfree.googlepages.com...testsandbiopsy


Being gluten free for a week or two before biopsy may not affect your biopsy results, but longer might. You need to be eating gluten for accurate blood and biopsy results. I know blood antibodies can normalize very quickly...falling sharply within one month.
Antibody levels in adult patients with coeliac disease during gluten-free diet: a rapid initial decrease of clinical importance. PMID: 15554953

How quickly do the intestines heal??? I'm not sure I've seen anything concrete on that, but it likely depends upon the degree of damage. Severe damage may not heal in weeks (in fact, can take 6-12 months or longer), but mild damage may heal more quickly. I'm going to look around to see if I can find any studies or articles that address this specifically.

How long have you been gluten free already, and how soon is the biopsy scheduled?