I’ve accidentally deleted a project file 
. I still have all the data files. Is it possible to re-create the project file somehow?
Windows XP Professional - Audacity 1.2.6
Thanks.
Two of you in one day 
See here: https://forum.audacityteam.org/t/losing-a-aup-file/26967/1
By the way, Audacity 1.2.6 is obsolete. You should update to 2.0.2 as soon as possible: http://audacityteam.org/download/