The final closing of the deal was revealed via Twitter by Microsoft's Harry Shum, the company's Executive Vice President for Technology and Research:
Excited to report we've completed SwiftKey acquisition.— harryshum (@harryshum) March 1, 2016
Welcome to Microsoft @SwiftKey! Let's do great things together for our
Microsoft has already confirmed it plans to keep supporting the SwiftKey apps on iOS and Android, and it plans to integrate its features into the Word Flow keyboard for Windows 10 Mobile.
Source: Harry Shum (Twitter)