Out of interest, what were the alternatives? As much as I'd love a world in which we were on Lisp machines or running Dylan, these weren't exactly alternatives to C at the time to my knowledge.
Before C was brought into the world, OSes were being written in Algol, PL/I dialects, since 1961.
At Xerox PARC they moved from BCPL into Mesa, used to write Xerox Star and Pilot OSes. Also one of the first IDEs, also known as Xerox Development Environment (XDE). The year was 1976.
Mesa eventually got automatic memory management support (RC with a local tracing GC for collecting cycles) and became known as Mesa/Cedar.
Niklaus Wirth created Modula-2 in 1976 after his first sabbatical at Xerox given his experience with Mesa, used it to create the Lilith workstation at ETHZ, this was followed a few years later by Oberon for the Ceres workstation, inspired by Mesa/Cedar after his second sabbatical at Xerox.
The OOP extensions that Borland added into Turbo Pascal are actually from Apple's Object Pascal, used to create Lisa's OS and the initial versions of Mac OS, before Apple decided to make the development tools appealing to the growing UNIX workstation market and introduced Macintosh Programmer's Workshop.
On MS-DOS compatible systems, which were written in Assembly, there was a plethora of Basic, Pascal, Modula-2, C and C++ compilers to choose from. Plus business languages like Cobol and xBase.
It was only with the success of Watcom C++ adoption among game developers, thanks to its DOS extender, and the move to OS/2 and Windows 3.1 that C and C++ started to grow in adoption.
However most developers on OS/2 and Windows 3.1 were actually adopting C++ frameworks like CSet++, OWL and MFC, or alternative environments like TPW, Delphi or VB. Mac guys had Powerplant.
On Windows 3.1, C++ patterns like RAII were already common place, and even though each compiler had its own library, all of them provided support for safe strings, vectors and some form of smart pointers.
Writing pure C on Windows, besides Microsoft themselves, has always been mostly done by those porting UNIX stuff into Windows.
Even Microsoft by the time they released the Windows 3.1 SDK, a new set of macros was introduced to try to make it safer to code in plain C.
