If the 60 billion is not legally binding, of course the Uk doesn't have to pay.
So, if that genuinely is the case, it should reduce the cost of Brexit.
Hopefully, legal opinion would be unanimous, which would mean one less item to negotiate over.
However, if there is a difference of legal opinion - and expensive lawyers can always seem to find extra work ! - that could go to court, which would cause delay.
Don't get carried away about how much losing UK annual budget contributions means to the EU:
The net contribution is about 0.7% of UK GDP and quite a bit less than that % of Germany's.
The current EU net payers will divide the Uk's share between them. They aren't delighted, but it's hardly disastrous for them.
Similarly, about 44% of Uk exports go to E27 countries, whereas about 8% of E27 countries exports go to the UK.
The most effected E27 country would be Germany, but German business leaders have publicly said they want the EU neogotiators to keep to the "4 freedoms" because their business priority is a strong single market, not one weakened by special deals.
Failing to reach a trade deal would be worse for the UK, not just because damage to the EU is spread among 27 countries, but also because they have a large number of trade deals with other trading blocs.
In contrast, the UK would have no trade deals with anyone and it would take few years to negotiate them.
Even the WTO option is complicated, because all 190 or so WTO members have to agree to the UK's new schedules and some might disagree or block the UK until they get concessions.
very beneficial to both sides, but only if very clever negotiators can find
The best outcome is a transition arrangement like EEA / EFTA, so the Uk has a few years grace to plan properly for the longterm and negotiate trade deals with non-EU countries - including the US of course.