This will not affect you as long as you have 3CX v16 Update 7 or later. In that version, when Dynamics returns a new access token, it also returns a new refresh token, and 3CX stores this updated refresh token. As a result, you will always have a relatively new refresh token, which has a 3 months lifetime, so you will be OK with this.
In previous versions of 3CX, we weren't able to update the refresh token. It was obtained from the 3CX console when you press the Authorize button, and the same refresh token was used after that. So in this case, after 3 months of having granted access, you might have authorization issues, and the integration might stop working.