If I have a large number of static pages, do each of these urls "need" to remain in my sitemap file(s)?
Many of these have been indexed by google quite awhile ago. Will google drop them from the index if the url is removed from the site map and the bot never finds another page on the site that points to it?
Just looking for guidance on whether have so many pages in my sitemap hurts us or not. We've talked about reducing the number of sitemap files down into the thousands with only new content pages. Not sure if this is the right way to go.
I can only reply from my own experience with a much smaller website. I neglected to add a certain URL when I uploaded my sitemap months ago. I don't often visit that page, but after the last PR update I noticed that page had lost it's PR and no cache was available. I immediately added the missing URL and the next time my site was spidered it was found and re-indexed.
A Sitemap file augments our normal discovery crawl. If you submit a Sitemap, we don't exclusively crawl from only that -- it's simply additional information. You can definitely submit a Sitemap file with only new content and it won't hurt your other pages.