Some effects of the mirror imperfection could have been reverted, others not.
Citing from a workshop on HST image restauration: "The fundamental loss of HST imaging science as a result from spherical aberration is not a loss of resolution; rather, it is a loss in the ability to detect faint objects, especially in crowded fields."
On this workshop, different approaches to enhance HST images were presented. A deblurring by deconvolution was possible in this specials case because of a peculiarity of the error: The mirror mapped stars on the WFPC sensor as "tight core containing about 15% of the light, surrounding plateau containing most of the energy and tendrils extending in apparently random directions". The "core" provided enough information to restore resolution. The processing was done on the ground.
HST was designed with replaceable instruments in mind. Leaving the error uncorrected for new instruments was never an option, but fixing it in different ways was, as can be seen from a long list of options in the appendices of the Report of the HST strategy panel
No new technologies were developed since 1990 that would allow for the reversal of a lossy signal transformation.