Nearly New Northern MN Slab In-Floor Heat Home Needs New Water Line
Your options:

1) Add perimeter baseboard hot water heat units. Just re-route the existing master bath feed to these baseboard units.

2) Add perimeter electric units. This would be more expensive in the long run as electricity is more expensive than gas. Plus the installation would require added wiring. You could also opt for under tile electric heat.

3) Depending on the flooring in the master bath, you could tear it all up (or pour over it) and add ½" pex tubing on top of the existing slab and pour an additional 1" of concrete or gypcrete on that. This would require raising the entry door frame or cutting an inch off the door and a transition at the threshold. Aesthetically, not very pretty.  

4) Or, remove the entire slab in the master bath and re-pour the whole thing with new tubing in the slab. This option would be the most expensive but would leave you with a seamless repair.

The cheapest option is to add perimeter hot water heat to the master bath. You could even add a hot water towel warmer that would actually add something to the repair. Unfortunately, the baseboard heaters will look out of place in a slab heated home. 

Good luck!