Some former Be employees have commented here in the past saying that Apple made the right decision to buy Next and not Be from a technical perspective, as BeOS had poor code quality and was far behind NEXTSTEP in important areas like networking and printing. They also implemented the OS API directly in C++, which tied them to a specific C++ compiler (some mid-90s version of GCC) due to the ABI getting broken in newer versions. The 32-bit version of Haiku (modern BeOS reimplementation) supports BeOS software, and as a result still needs to be compiled with that mid-90s GCC release.

Beyond that, I'm not sure if buying Be would have fixed the managerial problems at Apple. Would they have been able to add the required features to BeOS to turn it into a production OS without the project turning into another Copland? Would the existing Apple management have slimmed down the massive Apple product line that had dozens of nearly identical models? Would it have gotten rid of dead-end projects like Newton and Pippin? Etc.

Designed in California has been a very entertaining (video podcast) watch that covers this era:

https://www.youtube.com/@designedinca

(Specifically they talk about Be beginning: https://youtu.be/5IFxwnXASyQ)

They probably would fail to recover and be another historical company by now.

If not, desktop computing would be taken over by C++ as main systems programming language, and UNIX like computing relegated to servers.

It would have been a disaster, BeOS was significantly different from a NeXT/BSD-like unix type base that made it relatively easy for software to be developed on MacOS in the 10.0 to 10.4 era. Early versions of MacOS X like 10.0 were clearly just an evolved NeXT with a cute MacOS finder like skin on top.