EDIT: Apologies. Updated with a link to what gorhill REALLY said:
Manifest v2 uBO will not be automatically replaced by Manifest v3 uBOL[ight]. uBOL is too different from uBO for it to silently replace uBO -- you will have to explicitly make a choice as to which extension should replace uBO according to your own prerogatives.
Ultimately whether uBOL is an acceptable alternative to uBO is up to you, it's not a choice that will be made for you.
Will development of uBO continue?
Yes, there are other browsers which are not deprecating Manifest v2, e.g. Firefox.
Brave has added a feature to explicitly enable MV2 apps and install uBo directly from Brave settings. You can also install uMatrix and Adguard MV2 versions also.
There are plenty of browsers built on Gecko that aren’t fire fox. So if you don’t trust Mozilla to build your browser, and don’t want your ad blocker bricked by Google, you have options.