"Why would database software be written such that deleting an ancillary file ( such as a log file of historic steps) cause it to fall over?"
Not familiar with that particular engine but one possibility is that it contains the log of current transactions, i.e. WORK that's STARTed but not yet COMMITted or ROLLed BACK. That puts the engine in a bit of a quandary as to what it's working on. The longer term need for the logs is to roll the database forward after a restore from backup and there ought to be a means of archiving logs for use as and when required instead of letting them grow indefinitely.