Get as much documentation as you can. Ideally you'll have a detailed billing statement with all DIDs on it and a Customer Service Record (CSR.) The CSR is a spreadsheet that contains a list of the underling carriers and billing info for each one of your DIDs. This can be surprisingly inconsistent especially if you've added numbers over time. It can be used to complete number ports if there are disputes. In a nightmare scenario you can take you billing statement and CSR and use it as evidence in an FCC complaint.
IMHO: the most likely scenario is that your local provider get gobbled up by a bigger player.