Is it safe to leave a gas oven on unattended?

The US Fire Administration clearly recommends not leaving cooking appliances unattended when no one is home:

Based on 2006-2010 annual averages:

• Unattended cooking was by far the leading contributing factor in home cooking fires. [...]
• Ranges accounted for the largest share (58%) of home cooking fire incidents. Ovens accounted for 16%.

At the time this related answer was written, the Fire Administration said (they have since updated the page):

The leading cause of fires in the kitchen is unattended cooking.

• Stay in the kitchen when you are frying, grilling, or broiling food. If you leave the kitchen for even a short period of time, turn off the stove.
• If you are simmering, baking, roasting, or boiling food, check it regularly, remain in the home while food is cooking, and use a timer to remind you that you're cooking.
• Stay alert! To prevent cooking fires, you have to be alert. You won't be if you are sleepy, have been drinking alcohol, or have taken medicine that makes you drowsy.

In terms of the chance of your oven catching fire/exploding, I don't believe that whether you are there or not would not make much difference. The only difference you watching the oven makes is that you can respond if it were to catch fire - saving your house. (I suppose there are some cases where your oven would start smoking, which would make you turn it off)

Oven technology is fairly well developed, especially the fail-safe devices, but there is always the possibility that the fail-safe fails (especially as you probably have a slightly older oven, having mentioned pilot lights).

Overall, I would say that you'd probably be lucky if you did leave it on all day, however, with your house hanging in the balance, I would advise you to play it safe, and monitor your oven.

(I realize that some recipes take a long time, but reducing the cooking time, perhaps by reducing the size of the thing you're cooking, would be preferable to leaving an oven unattended)