What would be best topology considering that:

1. 6 x Exchange 2010 Standard Licenses
2. 2 x Separate locations that are supposed to support redundancy in case of link problems
3. 4 x Forefront TMG 2010 with Forefront Security and Forefront Protection/Security

Multiple locations worldwide using those Exchange. Most locations will be connected with VPN Tunnel (the ones hosting Exchange for sure).

I was thinking something like this:

Location MAIN (about 70-100 people):

1. 2x TMG 2010 in NLB
2. 1x Exchange 2010 CAS/HUB Role
3. 2x Exchange 2010 Mailbox Role (Active + Passive)

Location SUPPORT (about 20 people):

1. 2x TMG 2010 in NLB
2. 1x Exchange 2010 CAS/HUB Role
3. 2x Exchange 2010 Mailbox Role (Active + Passive)

Management wants to make sure that in case of problems in main location (power failure, link loss etc) second location can support all traffic from around the world and vice-versa. We have 6-7 locations and more comming up (not big ones but like 10+ people per each location).

I do know that CAS/HUB is single point of failure (and no NLB), but i simply lack more licenses to do some redundancy on that.

What do you think about this approach? What would be better approach according to you?