In either a criminal or civil trial court, what happens if the judge keels over on the bench? Is it an automatic mistrial? Or can a new judge take over in the middle?
Generally speaking, it’s not an automatic mistrial. As a neutral arbiter, theoretically a new judge can seamlessly step into the robes of a…er… departed one without causing problems. And if we’re talking about a two-day trial, that’s probably true in fact.
A horrendously complicated trial, replete with pre-trial rulings that depended on what was ultimately adduced at trial, however, might well be too much to foist on a new judge and a mistrial might be the only possible result. In the criminal world, such a mistrial would not likely server as a bar to reprosecution, since it was not at the behest of the prosecution. (And from a practical standpoint, a contrary result would guarantee that an accused criminal could guarantee his freedom by murdering the judge…not exactly the wisest precedent to set.)
I would assume they remove the body from the court room 
From the Ohio Rules of Civil Procedure, Rule 63(A):
If for any reason the judge before whom a jury trial has commenced is unable to proceed with the trial, another judge, designated by the administrative judge, or in the case of a single-judge division by the chief justice of the supreme court, may proceed with and finish the trial upon certifying in the record that he has familiarized himself with the record of the trial; but if such other judge is satisfied that he cannot adequately familiarize himself with the record, he may in his discretion grant a new trail.
Crim.R. 25(A) is the equivalent provision for criminal trials.
I’ve never heard of a judge dying or becoming disabled mid-trial in Ohio, but I suppose it must have happened sometime.
I expect they’d make a Hollywood thriller out of it, where the sassy female juror links up with the handsome defence attorney to show that the bailiff actually did the crime, but has framed the accused, except the judge found out about it and started blackmailing the bailiff, who got his brother-in-law to kill the judge using a crafty method that only the sassy female juror recognises once the trial restarts but how can she communicate this to the handsome attorney because the jury is sequestered…
Ask a question, drag the judge. Ask a question, drag the judge…
Hmmm, doesn’t port to well. 
Federal Rule of Civil Procedure 63 similarly (imagine that!) provides that “any other judge may proceed” if such can be done without prejudice to the parties. In a non-jury trial, the successor judge may recall witnessess at the request of a party or on his or her own initiative.
This was done in the episode Matlock Meets Diagnosis Murder in Murder 101 with Dick Van Dyke playing both Dr. Mark Sloan and Dr. Jonathan Maxwell, and his son plays both of his regular sidekick roles plus the dead judge, wearing a white Brit fake wig.
I think I saw that one! Or maybe my great-grandmother just told me about it.
Damn! It’s so hard to come up with something new…