I’ve gone back and restored the individual archive links, and reformatted the monthly archives to be chronological lists of links to each month’s entries. Now all the MT permalinks are back in operation, and I haven’t overloaded my disk space (which, I confess, I need to bump up some more so as to avoid problems like this in the future).
Update: Just changed plans from 25mb to 200mb. I think that ought to tide me over for a while, disk-space-wise.