What Philipp says, but I'll add the consequence of a EU regulation ceasing to be enforceable law in the UK, without having a replacement in place, would mean lawlessness in that area.
In many cases, there will be a UK law created that is identical to the EU regulation, so on the day that the UK leaves the EU there is no actual change in the law. If the government isn't happy with some of the current regulations, they can change the UK law at leisure over the next 50 years. There would just be no time to do this over the next two years.
There will be EU regulations, estimated 10%, that cannot just be copied word by word and made UK law, because they refer to the EU in a way that wouldn't make sense in UK law. For example a regulation might say "in situation A, EU regulation X applies". You can't make this UK law. The sentence has to be changed to "in situation A, UK law X applies". Doing that for 1,000 or so regulations costs time, and of course all 10,000 or so regulations must be checked. You can't rush this, or you might end up with some ridiculous laws if mistakes are made in the process.
Now I am totally annoyed and angered with the whole Brexit situation, but what I wrote is just common sense: If the UK leaves the EU, then what I described above must be done. If the Scottish government rejects this bill, then either May finds a way to still implement this bill, or there will be a total disaster the day the UK leaves the EU. But then the only reasonable way to avoid that disaster is to delay the actual exit. (The other EU members could rightfully say that this isn't their problem and refuse a delay).