Presumably the base of the chimney is brick or concrete block. Water ingress itself into these materials will not affect the structure of the material, especially over a relatively small timeframe. The problems would start if the water in the brick/block froze, but this probably hasn't happened - if it had, the face of the bricks would show distress.
If it has only been for a few months, you will be ok - even with the surrounding timber. Dry it all out (obviously stop the leak first!!) - preferebly with a dehumidifier around. Plaster is very susceptible to water damage, so you might have a bit of patching to do, followed by some re-decoration, but in that timeframe, I can't envisage any serious damage. Make sure everything is completely dry though - not just surface dry.
Del
