Dependant on Tier 2 visa

[expositouk1]

Hi folks,

I will be very grateful for advice on a friends behalf please? He's not very computer savvy so he can't post here himself.

He is on a tier 2 visa with his wife as dependant. Their visas expire in about 3 weeks time, but having found out about a string of affairs by his wife in the last he's taken the decision not to renew her visa for her so she goes back to their home country. However, it looks as if she's got no intention of leaving the country. Could someone kindly advice on these 4 points, please?

1. Does my friend have a legal responsibility to notify the UKVI/Home Office that she's no longer his dependant once her visa expires or is that the lady's own responsibility?
2. Does he have a legal responsibility to facilitate her departure from the UK (buy her air tickets etc), or is he in any way responsible to ensure that she leaves the country?
3. They have a 3 year-old son who is meant to travel with her back home. In case she decides to remain illegally, does this affect the child's prospects of getting another visa the future (once his father gets indefinite) in the same way as it would affect her mother as an adult who has breached the immigration rules?
4. Could someone kindly provide a link to the Home Office website which gives advice on such situations, please?

Thanks for your wonderful work!