Protect 555 timer from high voltage
I suggest using a combination of clamps and separation by other semiconductors being in the way. 







simulate this circuit &ndash; Schematic created using CircuitLab

Something like that - to protect the 555 pin from inductive kickback, output voltage swings, separation by the totem pole driving circuit (which is a nice high-power fast switching bonus too) and clamp over the MOSFET to protect that, plus a clamp over the transformer.

Its as little overkill, but I think it's crazy enough to work! I hope others can critque/improve upon this suggestion.