I too don't know how i would/will cope in this situation.
I too believe you have to allow yourself to fall in love with them - how can you not.
Our 2 lo's turned up with a teddy and their toothbrushes in hand - nothing else. That image makes me cry now and I think will stay with me always.
Some people already are saying 'oh, i couldn't look after 'other peoples' kids'.. my answer is that it doesn't matter - they are "kids" - it doesn't matter past that.
In theory I think that well, i have to let them go, it was always part of the deal, and to let them go will make room for new ones, but I can imagine myself now sobbing typing messages on here looking for a way to cope.
You sound like you have done amazing things - you should be very proud of yourselves and I'm sure he will be in your hearts forever. I wish I could say losing the first will be the hardest, but I think if you do your 'job' (ha) properley, it will never get easier.
From the sounds of yet, your days won't be quiet for that long if social services are worth their salt - they'll be asking you to take on more in no time.
From a very inexperienced carer, a HUGE HUG to you all.. talk about the hardest job in the world!!! Hold on to the good you have done, and have in you still to do for some other lo's.
:)