Normally I'm the sort of person who is meticulous about redirects - quite obsessively so - if I remove a page I put up a redirect. I'm now faced with a situation where a whole site is being completely restructured and redirecting each page won't be physically possible, from both a time point of view, and even if it was it would result in a giant .htaccess file which I understand isn't ideal.
What I've been told to do is just redirect the key important (high traffic) pages and not worry about all the rest - just try and put some redirects at directory level where possible. I'm just wondering what sort of effect that might have in Google - will they deem that our whole site has become horribly unreliable and will it damage rankings for even the pages which are redirected properly?
I'm also wondering if putting in a redirect to a page which isn't appropriate is worse than just leaving it to 404, both from the user and search engine point of view? Obviously we need to make our 404 page user friendly as well.