Windows Phone 8.1 owners who upgrade to Windows 10 Mobile will still be able to downgrade

Microsoft began rolling out the Windows 10 Mobile over-the-air update to selected Windows Phone 8.1 devices in March. However, if those folks that do receive the update decide that Windows 10 Mobile is not for them, they will continue to have the option to downgrade back to Windows Phone 8.1.
Jason, a member of the Windows Insider Engineering team, offered up this news via his Twitter account (via MSPoweruser):
@NorthFaceHiker Mr, When will be available W10M in the WDRT ?

@heynerandresgom Devices that originally launched on WP8 will keep WP8 recovery images in the tool.

This is good news for people who might encounters bugs and other issues with Windows 10 Mobile, or if they just like Windows Phone 8.1 better. Jason also confirmed that there are currently no plans to offer Windows 10 Mobile images via the Windows Phone Recovery Tool.