When you call it silly, it depends on the circumstances really.
Den's was ridiculous, because even though you didn't see his body drop into the canal, his death practically played out on screen. Den's return really shot the show in the foot in my opinion and ever since he returned, the show has been a mixture of good and bad.
Kathy's return wasn't so bad. Her death completely played out off screen and whilst it was out of character for Kathy to leave her Sons, it wasn't completely ridiculous like Den's and I did find it believable.
Nick's return was never really a 'Bringing back from the dead' storyline. From the moment the storyline started, it was hinted he as still alive.
Besides, I find decisions such as killing off Angie, Kathy, Pat, Cindy, Den, etc. In the first place much more bizarre than bringing them back from the dead