Totally understandable,
although for the things like fun and games stuff keeping the post count to something like 300-500 before it being restarted might make more sense and would allow more room and bandwidth for things take make take greater priority at that time. Usually things that affect the lives of the OP or the ones who are posting at that given time and may need more urgent responses.
although keeping it too low would increase the maintenance hours that people maintaining the site and servers need to put in.
as for persons post count going to low - can I suggest something like a base value and levels to that base value?
it would work something like:
a person with a post count of 100-149 gets a base score of 100 and the next base value/level after that is 150.
so how it would work is a person with a post count of say 509 gets a score of 500 and this number is then attached to their profile and the server then stores this value as level L or J or K and then this value brings up that score. and from that the datetime of the post that gave that person that value and from there the amounts of post are calculated using the count of datetime values assigned to each post.
That way the person doesn't loose too much numbers of post from their post score
example: if they have reached a post score of 461 out of which they made 96 posts in fun and games section. when that topic is taken offline rather than loosing 96 from their post score they only loose 11.
I don't know how this would work in reality but its just a suggestion, sorry if am rambling.
I have to deal with similar issues in RL. sooo can't help myself.

edit: yup and a lot of forums usually just limit it to 500 to 700 max.