A quick check shows me mice have strong homing instincts and can be back in the vicinty of your home within 24 hours (others can take up to two weeks). The tests were done on distances of 600-1200m. My inclination would be to release them in open ground ... a bit further than 1200 away. House mice are a public health risk as they carry diseases - your local council or authority may have a web page about pest control and what to do. The cat sounds like a good option, although they can also leave you small gifts of mauled birds and rodents.