All your work is saved in the catalog file. So if you decide to buy after a trial, nothing is lost.
The message relates to those who stop their subscriptions. In other words you can continue to use the Library, Print, Web, Slideshow etc but you cant do further editing because Develop & Map get disabled until you start subscriptions again.
A LR5 catalog will work in LR6 when you upgrade it during installation.
They mean something else. After the trial Lightroom 6 will continue to work, except for the map and developer. Lightroom 5 is independent of this. It will continue to work completely with its own catalog file (assuming you have a permanent license to LR 5) but you won't be able to access the catalog that you edited in Lightroom 6 with it.
1. If taking a trial for Lightroom 6 means that Lightroom 5 wil actually be ready for the trash (unless you like to do all the work done all over again), I do not feel like taking the risk.
Not ready for the trash at all. Your LR 6 edits simply will not be available in LR 5. You can try to save metadata to file in LR 6 and reading it in in LR 5 but not all edits will translate. So doing the LR 6 trial will allow you to play with it and test whether it would work for you, but if you are not sure you want to commit, don't transfer all your work to it.
2. If Lightroom 6 has a different development tool and maping module (resulting in loss for Lightroom 5) what does this actually mean ? I do hope it does not mean that all development history is bound to cloud working ?
There are a few differences but they are not so major in my opinion. One for example is that you can now edit gradient filters with a brush. The others are the new merge to panorama and merge to HDR features and the GPU acceleration which for many people that don't have super beefy graphics cards actually results in deceleration. For the rest, Develop is basically identical to that in LR 5. The app is not bound to cloud working. It just needs internet connectivity once in a while to check its license if you have the creative cloud version but it doesn't store edits in the cloud or anything like that. You can still buy a standard permanently licensed LR 6 version upgrade from Adobe if you don't want to do the cloud thing. They hide it behind many rocks but it is still there on their website.