The reference librarians at the local law library may help point you to the right resources to find the answers to legal procedural questions.

It depends on the type of case and the type of court appearance. It can be a default will be entered against you, and in certain situations, a...

You should get an attorney in the state where you were working, even if it is arbitration. Start with consuming with employment/wrongful...

Even if they can force you to trim the trees, it is unlawful to throw the tree debris into your property.

Consult with experienced probate/estate attorneys in the state where this occurred. A full analysis needs to be done to determine your rights.

Bring these serious concerns to your attorney in the case who can determine how they can best be used for your defense.

Yes. If they are still a party to a case, a request may be able require their appearance without an actual subpoena.

Depending on the fee agreement, the work done and not done, you may be able to recover the fees paid by a small claims lawsuit or initiating Bar...

If it was below the standard of care to leave it in and leaving it in caused significant additional harm, it could va a viable case.

Definitely if it was not an object that was intended to be left behind (for examples staples and pins are often intentionally left).