It may be less great if she goes off on this likely ill-fated venture, the stresses and disappointments undermine the marriage, and the marriage falls apart but by then she's produced a child (perhaps a couple?) by this guy. Custody battles, visitation, concerns over the ex.'s significant others impact on the child, etc...
If their business goes bankrupt, wonder what effect that'll have on her over time?
But to me, the biggest victim here may be the child that could come out of it.
If they do go on this venture, it would be fascinating to get an update from the OP in 5 years.
Richard.
Stop it you are making my mind numb with all the speculative fear. Let kids be kids. They are not joining some suicide club.