I get asked this type of question very often and I have had to answer this on for myself recently, though Euro-to-Pound in my case. Being an economist by training, when asked such a question, I put on my wisest face, square-off my economist's hat, get the questioner to sit down with me and I look them in the eye and say, "As an economist, I can predict anything, absolutely anything - except the future. Nobody can predict the future and only a fool would try!"
So, being a fool, let me gaze into my crystal ball -
I do not believe that Brexit will happen, as crashing out without a deal would also crash the economy and lead to a steady downward spiral of inflation and stagnation - stagflation was the buzzword of the 80s, remember?
A 'managed-no-deal' is not possible with this government or with this parliament, riven as both are with conflict, intrigue and breathtaking incompetence.
No sane government can risk crashing out, as the EU would be forced to allow the full consequences to befall the UK. With eurosceptic governments in the Eastern EU, it can ill-afford to allow the impression that leaving, but with a sweet deal in the pocket is in any way an option. Or as Voltaire put it "Dans ce pays-ci, il est bon de tuer de temps en temps un amiral pour encourager les autres." (In this country, it's a good thing to kill an admiral now and again, to encourage the others!)
So that just leaves May's non-deal (which looks more and more like no Brexit at all) or a second referendum, which realistically can only happen much further down the road - by which time the full unbridled consequences of leaving the EU would have filtered through to many 'undecideds' and only the hardened few will insist that Britain must go down fighting!
So, having wiped the gozz and phlegm off my crystal ball, that means that even greater uncertainty awaits the UK and the pound may sink even further in 2019 - but the medium to long-term prognosis is good. Once Brexit is out of the way, a great sigh will be heard and businesses can start investing once more and the pound will recover lost ground.
One thing to bear in mind is that a great deal of money is leaving the UK right now, fearing the advent of ATAD (Anti Tax Avoidance Directive) coming from the EU. All the leading Brexiteers are also 'off-shore investors' and have realised that even with an early Brexit, ATAD will be implemented in the UK. What consequences that might have for you, is a subject you might want to investigate.