It will do its thing and if it needs more time the frame-rate will go down ;). It won’t try to achieve a certain frame-rate and then skip things if it doesn’t have enough time.
If that is what you are asking? As far as I know, it’s save to render a sequence unless you don’t have enough video memory to load all textures used. You can try to disable “texture streaming” but it won’t give you more texture memory then you physically have and is assigned to the texture pool.