MKRT with 2 internet conections

Hello.

I want to implement MKRT with 2 internet conections:
/interface set ether1 name=Internet1
/interface set ether2 name=Internet2
/interface set ether3 name=Local
Some firewall mangle roules:
/ip firewall mangle add chain=prerouting in-interface=Local connection-state=new nth=2,1 action=mark-connection new-connection-mark=Net2 passtrough=yes disabled=no
/ip firewall mangle add chain=prerouting in-interface=local connection-mark=Net2 action=mark-routing new-routing-mark=Link2 passthrough=no disabled=no

/ip firewall mangle add chain=prerouting in-interface=Local connection-state=new nth=1,1 action=mark-connection new-connection-mark=Net1 passtrough=yes disabled=no
/ip firewall mangle add chain=prerouting in-interface=local connection-mark=Net1 action=mark-routing new-routing-mark=Link1 passthrough=no disabled=no

If internet connection of ISP1 will go down, what about traffic. It will pass throw ISP2 connection with no probles?

Ip proxy will works with that configuration?

Thnks a lot.