Laravel 5 on MySQL with MongoDB fallback

I am planning to create a website with possibly high amount of transactions. My plan was to have main information (users, purchases, etc) that have less frequent writing in MySQL and put high write information (ex. logs) into MongoDB.

However, I was wondering if there's any point in replicating the MySQL into MongoDB to server as a backup if MySQL falls down or whatever might happen? And if so, how would one go about to doing that, just a try-catch block around initial db connection to switch to other db automatically? Or is even the idea of such a double db in Laravel silly?

Thank you!

via Chebli Mohamed