I don't think Meagher was criticized by his peers for not leading the charge. Hancock's report makes it clear that he had mobility issues and didn't take issue with it. The only embarrassment Meagher suffered was that an officer of his brigade mistakenly told him that Hancock gave permission to retreat across the Rappahanock. Hancock was not happy about this but was more understanding when Meagher explained the events "candidly and fully".
In any case, Meagher seemed to have been burnt out by the heavy casualties suffered by his brigade, the army's refusal to allow him to bring the Irish Brigade home for recruitment. He ultimately resigned his commission after Chancellorsville, complaining that the army was wasting his gallant Irishmen.
He then changed his mind, asking to withdraw his letter of resignation on July 13, 1863, and tried to recruit a whole new brigade. He was not very successful in this effort and his status in the army was unclear until just before Christmas 1863. He then got word to report to Washington in late spring 1864 and then to City Point for assignment. Grant didn't really have a command for Meagher and then finally found one in the Western Theater. Unfortunately, Meagher had insulted Sherman, publicly calling him an "envenomed martinet" after First Bull Run and Sherman never forgot.
He was given the Provisional Division of the Army of the Tennessee, with the job of guarding the Chattanooga and Knoxville Railroad. His division was later called on to reinforce Sherman at Savannah (later changed to Fort Fisher), but the transfer was something of a disaster. When the division arrived, it was "a mob of men in uniform" without any wagons or any sort of transportation. The whole thing was so bad that Grant had him relieved.
On Meagher's death, while there are many interesting theories, I am most inclined to believe it was an unfortunate accident. He was badly ill with dysentery, feverish and probably needed to relieve himself. With safety standards being absent in that age, it's not hard to imagine that he lost his footing and fell to his death.