UPDATE: I just tried to reinstall the MySQLi extension and got the error message: "Cannot find the data for the database; therefore extension will not be installed". Now what?
You can roll back to a previous version of Dreamweaver, but I would imagine it's a real hassle. What you learn is to NEVER install the latest version of Dreamweaver until you get the all clear on here that it works with the WebAssist extensions.
Regarding your urgent PHP update, is it something simple I could help with or is it bigger than that?