Sadly Laura's passing has stalled the legal challenge but there are good legal avenues for successfully overturning the law in the future. I can think of three off the top of my head there may be more.
1. The fact that it is likely to be considered ( in line with the Canadian Supreme Court) to be a breach of an escorts Human Rights. Given recent reports of violent attacks on escorts this is likely to succeed
2. As JT has mentioned the fundamental asymmetry which allows for the sale but not purchase of sex may well be in contravention of the constitution. A Former AG and a Justice Minister believed this to be the case.
3. The argument that criminalising consensual sex for money between adults out of the view of the public may be a breach of privacy rights. Probably the weakest of the approaches but may run as there are a number of favourable decisions from the past which could be quoted.
The supporters of this legislation put a lot of stock in the conflation of Human Trafficking with all aspects of the sex industry. This is of course an unproven assertion and a cogent dismantling of this link would be a central part of any legal bid in the future.
The radical feminist perspective that all sex for money regardless of the circumstances is essentially a form of rape, is also embedded in the thinking behind this legislation, but IMO would be relatively easy to undermine under legal scrutiny.
I would give a properly funded and competent challenge at least a 50-50 chance of overturning this legislation in full or in part.