Dear Lord, you could have him be a fighter for the TARDIS. :\
If it were up to me I'd put him in with the break model of the Baker-era TARDIS, along with the console and TARDIS walls.
And if anything should be used for TardisDeath, I'd choose that sound clip from when the Tardis breaks in The Mind Robber.
That was initially the plan.. do a set of skins for my new TARDIS to match the original, Pertwee era, Baker era and maybe McCoy era skins. But I was also thinking of him being in the regular break mod more like an Easter Egg.
K-9's nose laser is actually the color of a PH-3---bright red. Every once in a while they would slip in another color to represent stun or some other setting. The TARDIS prop was the same prop all the way through Hartnell, Troughton, Pertwee, and partway through Tom Baker. The one and only change done to the original TARDIS box was that the St. Michael's Ambulance Society decal on the door was painted over early in the Hartnell era.
I believe it was in
The Hand of Fear that the beat-up old police box finally collapsed and damn near brained Elizabeth Sladen (Sarah Jane Smith) when the roof fell in on her. After that they built a new TARDIS prop and it underwent a number of minor changes over the years. The roof had different slopes, became a stacked roof, the light on top changed a few times and the color/patina changed as well, from lighter and newer-looking to darker and battered. Oh, and don't forget about the one episode with the infamous blue flashing light on top.
And if you're going to do a Who-related TARDIS destruction sound you should go with something really impressiv and use one of the "TARDIS take-off malfunction" sounds. You know, lots of scraping and beeping and bellowing and grinding. Sort of a "We've got to get out of here, Doctor!" "I'm trying!! Oh, these stupid controls!!!!" "Doctor, hurry!" "Too late!!!!" Kaboom!
Here are a few good materialisations/dematerialisations for you to try out.
(This one is probably your best bet. The sound is taken from
Spearhead from Space and was a sound effect for the Doctor's first attempt to escape his exile to Earth in the TARDIS. Needless to say the take-off was unsuccesful in the extreme.)
Or you could just say "Eat hot death, Beeblebrox!" and do something really clever and original.