OpenOffice and LibreOffice are already "merged". In fact in the past years, after the fork, LibreOffice developers regularly tracked OpenOffice source code repository and merged all the useful changes they could find, by either picking the original code or re-implementing it their own way.
In addition to that they also completely overhauled and simplified the build system, removed tons of dead code and translated German comments which where there since StarOffice, replaced Java components with equivalent ones written in C/C++, are in the process of switching from GTK2 to GTK3 (mandatory to get Wayland support in Linux), etc. Doing so they made the LibreOffice source code base sustainable on the long term and lowered the difficulty entry level for new contributors, while apparently OpenOffice buildbots are not even able to rebuild their software since last year...
The only useful asset which remains to OpenOffice is the trademark.
In addition to that they also completely overhauled and simplified the build system, removed tons of dead code and translated German comments which where there since StarOffice, replaced Java components with equivalent ones written in C/C++, are in the process of switching from GTK2 to GTK3 (mandatory to get Wayland support in Linux), etc. Doing so they made the LibreOffice source code base sustainable on the long term and lowered the difficulty entry level for new contributors, while apparently OpenOffice buildbots are not even able to rebuild their software since last year...
The only useful asset which remains to OpenOffice is the trademark.