Angelo regenerating at the beginning of Series 3 was borrowed from Doctor Who (1963). Tyler Butterworth was replaced in the role by Tim Whitnall who played Angelo up until the finale.
Shelley Thompson (Rita King) remained in the series until Series 6 and was replaced by Katy Murphy as Katy Andrews who remained until the finale.
Tyler Butterworth left the show at the beginning of Series 3 and was replaced by Tim Whitnall. It was written in (#3.1) that Angelo feels ill which he succumbs to his illness and dies and he regenerates and is given a new face and a new body.
Michael Benz replaced Matthew Wright.
The 1999 series explained what happened to Mike Mason and that Mike Mason went off to America and Angelo and Katy reading a postcard he sent them.