I would say not to panic just yet.
We can't have hard brexit if a50 is deemed unable to be triggered by royal prerogative. Throwing it back to Parliament will ensure hard Brexit will not happen. a50 is frankly not fit for purpose and there is a high chance this will become increasingly apparent especially if the legal challenges to a50 are successful (which again is pretty likely).
Talk of hard brexit I feel strongly is nothing more than posturing and to appease the hard right at this stage. Its to set up the UK for negotiations. It is to force the EU to realise the situation the UK is in constituentially and how using a50 as the exit is also not in their interests. It is to protect May in the long run from accusations that she was a Remainer. If the legal and democratic system takes much of the decision out of her hands and forces a much softer exit then she is still seen to have been committed to hard brexit, it was just those other remainers than made her do it.
I believe we are more likely to get to a situation where a50 can not be triggered because its not fit for purpose, and is in compatible with the British Constitution (or lack of) but under EU law, the EU is obliged to recognise the will of democracy thus forcing an alternative way of exiting the EU - probably though some sort of new treaty which either allows us to stay in the EU under different terms (possibly the formation of a two tier EU) or to exit under terms which aren't bloody ridiculous for both the UK and EU partners.
In order to satisfy EU law as being the will of democracy this treaty would have to be thrown back to the public in another referendum. Of course we could reject this; this would throw both us and the EU back into another constitutional crisis.
The fact that a50 has even ended up as a court issue rather than simply being triggered means that legal issues are now driving this rather than political ones. An immediate triggering of a50 would have effectively bypassed this, but the outcome would have been pretty much economic, political and legal meltdown (not dissimilar to those evil predictions of 'Project Fear' I suspect). It also could have been found retrospectively to be an illegal act by the PM which of course would have had a few major ramifications. You'll note how many hard liners wanted to go down to route despite this. It says a lot about their respect for democratic and legal process which is more than simply a vote to leave or remain.
Businesses are making plans under the assumption of a hard brexit or prolonged uncertainty. An acknowledgement that a50 is useless, would be helpful. I think this is currently pencilled in for next month with a NI challenge in court in the first/second week and an English based crowd funded one due the third week.
Until the courts decide about a50, the government is really unable to start policy making as the exit route will make such a huge difference to the eventual outcome.
I suspect we will get an exit, but it will be a long game in order to preserve stability which will hopefully help with all those contingencies plans being drawn up at the moment due to the current limbo. I think it unlikely that we will have left the EU by 2020 though which will not please many. Its simply unfeasible for a huge variety of practical reasons with are both UK and EU based.
I think things will be become a lot more clear in the next 6 to 8 weeks. I don't think that hard brexit is inevitable at all. I think it is still a possibility, if the EU are difficult, the court rule in favour of the royal prerogative or Theresa May has a screw loose (this is something I'm not ruling out). I would suggest that she is however doing exactly the same as all the rest of us right now and playing the waiting game. I don't think she has too many other options open to her politically.