What will happen to my 640xl if..?

[Sumukh Phalle1992]

What will happen if I won't downgrade to WP8.1 before updating to Windows 10 Technical Preview (10.0.10549.4) from 10536?

 

[Skamath]

It is the land of the unknown Sumukh. If MS says do it just do it there would be a sound reason they say it needs to be done. Could be a glitch of sorts which might end up bricking your phone.

 

[Zachary Boddy]

You might not even be able to see up the update from 10536, or maybe you can but the update is guaranteed not to complete.