Yes, in the sense that anything which "denies service" is a "denial of service".
The CIA Triad defines information security as anything which affects Confidentiality, Integrity, or Availability of the system / data.
As pointed out in comments, this is not always an "attack" since it's just as likely to be accidental. Whether this is the result of a malicious attack, an admin botching a patch install, or the building catching fire, DoS due to data loss is definitely a security risk for which organizations should have a plan in place.
Assuming it is an intentional attack, if they have enough access to the backend server to delete db files, then there are far more subtle and nefarious things they could do (like stealing the db, selectively deleting data, planting a network sniffer, etc), so a DoS is pretty much the least dangerous thing in the category of "attacker has write-access to the server's filesystem", which is why "deleting the database" is to "DoS" as "canoe" is to "vehicle": not the first thing that comes to mind, but technically counts.