Why did she leave the series after only one season?

Did Jean Smart or Delta Burke ever make guest appearances after they left the show?

Apparently Julia Duffy was not happy and neither were the producers. the character Allison Sugarbaker did not turn as was expected, so they parted ways. Julia Duffy is a very talented actress and loved her in Newhart. However, Duffy had to disadvantages working against. First, she came had fill the shoes of Delta Burke and her Character Suzanne, which was impossible to begin with. Second, she was coming into a terrible environment following the Designing women war between Burke and the producers. Sadly, Duffy had alot going against her that was beyond her control. :(

Neither Jean nor Delta visited after they left.