I feel so bad for you and your family, I have been following this post and updating my husband every day.......I feel almost like this is our loss too.
Even though no boxer could fill Sebastians shoes,
I don't recommend waiting a long time to get another Boxer. They are great dogs, always have been my favorite breed, and I am sure that the love and care spent on Sebastian could make another dogs life very happy and your's too.
It is people like you, that care and do everything you can, that make the best pet owners, and any animal would be lucky to have you as theirs.......... I have been and will continue to pray for you.
anbuh