I'd really hope nothing happens to any of my cars. As it is now there are replacements I'd rather have, but they are a lot more expensive (Paseo -> Insight, Matrix -> Prius). I don't really have a wasteful/excessive vehicle (that runs at least), so my current vehicles I'm very happy with and are quite ideal. However, I'll play along.
If the Paseo died on me I probably wouldn't replace it right away. It gets driven very little lately. Last time I filled it up was about 3 weeks ago. I could probably get away just working on getting my '93 Tercel (not fully assembled currently) back on the road.
If the Matrix died on me I'd seriously look for a used Prius, but I doubt I'd find one. Other than that, I'd consider downsizing to the Fit if it met size requirements for hauling the wife's work equipment. If neither of those worked out it would be another Matrix with a 5 speed without a doubt.
BTW, list of current vehicles:
03 Toyota Matrix
97 Toyota Paseo
93 Toyota Tercel
82 Honda CM400
73 Jaguar XJ12 (restoration project)