If you're worried about losing a huge amount of links all at once then why not take a staged approach to pruning them back?
Personally I'd probably do some basic checks and try to figure out which sites you can guarantee won't be passing much value. Depending on the scale of your operation you might be able to do this by hand by checking for sites that have been grey-barred or pages that are no longer indexed. If it's a larger campaign then you'll have to use the metrics that are available to you to whittle down your list.
Following that I'd split out the campaign by page to see how much you're spending on each page and how much that page is worth to you on a monthly basis. This way you can start removing links from a high cost/low return page and if there are unexpected consequences it's less likely to cripple your site.