For 18.04 - no. The desktop will receive patches and stability fixes but these will not break anything that is running currently.
Given the current state of development of budgie desktop v11, 18.10 - and possibly 19.04 will then just see 10.4.1 or what ever patch to the 10.4 series is available. Again - this will not break any existing applets.
For budge desktop v11 we just don’t know because there isnt anything concrete here to work on. We don’t know what toolset is being used because it is being re-evaluated. So we cannot begin to update anything until this becomes more clearer.
Equally, we don’t really know what capabilities will be in a future budgie desktop v11.x. I would hesitate a guess that some of the current applets may be supplanted with equivalent or better budgie desktop v11 capabilities such as windows previews and better workspace management.
Thus there is a whole host of unknowns at the immediate point in time - things will obviously become more clearer in time but I’m hoping for great things with v11 as I’m sure you are (and the community) is as well.