Ad 1. I was thinking of someone taking an affected mouse from New Zealand to Eurasia either as a pet (which is accidentally released, or is allowed to breed and one of the descendants is released) or intentionally to control a local population of mice somewhere. This would probably not be a single isolated event. The special gene is likely to be considered a desirable feature for pets and laboratory animals. By keeping an isolated 'normal' population (for females for breeding), you can ensure a steady supply of male mice with the special gene. They are guaranteed not to get pregnant, and they are guaranteed not to contribute to any problems of the crop-decimating type if released. The ideal pet. As a result, there would probably be continuing pressure through events such as this as long as there is easy access to males with the offending gene on any continent. (Regarding stowaways: I am not sure if they still play a significant role anyway.)
Ad 2. This begins with a valid point - though "not at all clear" is not what I would like to be associated with the fate of any endemic species. As to the bottleneck, this was under very 'optimistic' assumptions for the method's effectiveness - combined with the problems explained in 1. At the point where you accuse me of smoking something and link to Wikipedia, you actually misquote me by lifting a casual "inevitably" concerning extinction of mice in places outside New Zealand, applying it outside its original context to the question of bottlenecks caused by restoration efforts, and extending the scope to worldwide.
>> You'd also need to make sure that nobody releases their pet mouse with the gene after you have started reintroducing mice.
> Again, these buggers last like two years. Modified males will be readily detectable due to the number of offspring mice produce. Also, very few people capture wild house mice as pets (given they are literally $1 at the pet store), let alone capture them and go on to release them later.
I don't see how short lifetime and easy detectability of affected males under controlled conditions invalidates my concern of people continuously releasing small numbers of modified male pet mice. (See 1.)
Regarding your last paragraph: As much as I would like the damage done by messing with the fauna of New Zealand to be undone, I don't think it's responsible to counter it by messing with it in a way that could damage the fauna of almost everywhere else.