Well, some good news for a change!!!
I got the report back from the host and it turns out that the site was not brought down by a malicious attack, and it seems like it was unrelated to the email from the hacker who had accessed our database. The site was brought down by some very heavy over indexing by bots, which have now been banned by the server and they have made some changes and cleaned up things to prevent the resources from becoming overloaded and crashing our site again. The site is now showing normal levels of activity and they are going to continue to monitor it.
So now my problem is I need to find out how the original SQL injection was done and then block it. The SQL injection I talked about earlier may or may not have had any relevance to it, I just googled it and when I found that we did not have that patch, I applied it. From the reaction you guys have given, it sounds like it was probably unrelated to how this person got in, but any holes I can patch can only be a good thing.
To reiterate, my site is 2.3.4, but as there have been many other addons done, one of them could have also created a hole. Obviously the above patch was not there, so there are possibly other patches that have been missed along the way too, so I am not out of the woods yet!