Hello,
There are several ways to do it.
The easiest is to add 0/1+128/1 static routes to an interface and re-do Your 0/0 route to point to next table.
If You want the FBFed packet to be looked up in global table if FBF-egress interface is down, then here is the example for Your instance "UDP-Routes"
delete routing-instances UDP-Routes routing-options static route 0/0
set routing-instances UDP-Routes routing-options static route 0/1 next-hop 37.123.100.98
set routing-instances UDP-Routes routing-options static route 128/1 next-hop 37.123.100.98
set routing-instances UDP-Routes routing-options static route 0/0 next-table inet.0
HTH
Thx
Alex