Meraki MX failover Question

[SopheakMang]

Dear Expert , 

I have DC and DR MX deploy as VPN concentrator HUB 1 and HUB 2.

we have branches at MX 68.

HUB1 at DC is the primary , DR is the secondary HUB , so any traffic MX68 at branches would forward to HUB1.

i have test when we shutdown HUB1 at DC , MX68 at branches's route will change default route to HUB2 at DR.

my question is that , what if connection ISP VPLS at DC down , MX at branch can't reach to DC MX HUB , but DC MX HUB still up and can access to internet as normal , in this case , Meraki MX at branches would change route to DR or not ?

and if yes , how long that it will change the route ?

[ww]

Edit:

I did not read correct.

[cmr]

@SopheakMangI think you should be okay if the DC MXs are in concentrator mode and not routed mode (this is how we operate them).  If your hub MXs are in routed mode with the internet on a WAN port and the VPLS on a LAN then I think I'd agree with @ww