I am not your lawyer, and this is not legal advice, it is intended only as general advice that you may consider in deciding whether you want to seek legal advice from an attorney licensed in your jurisdiction.
Usually when I tell someone it is not worth it to pursue damages it is because the Tenant is insolvent or the amount recoverable wouldn't offset the legal costs of pursing it. That doesn't appear to be the case here. Depending on the amount of damages done to your property and how well the security deposit covers them, it may be worthwhile to pursue in court considering you have an additional argument of breach of the month-to-month lease.
If I were in your shoes, I'd consult a local landlord-tenant attorney about it. Do you have local real estate investor meet-ups where you could get a referral? If you go this route, you should ask the attorney:
(1) what amount he or she expects would be awarded in damages,
(2) what the process is for collecting a damages award if the Tenant won't willingly pay,
(3) what the fee structure is and what it will cost you to collect
If you hire an attorney, he or she may start by writing a demand letter to the Tenant explaining your legal position and demanding an amount of money to forego filing a lawsuit. This may work to get you money owed without the expense of actually going to court for it.