If the UK leaves the EU, either with Theresa May's deal or with no deal, what happens to UK trade with countries that have trade deals with the EU? Does it immediately go back to WTO rules? Or has the UK government managed to get replacement deals in place?
If there is no deal then the UK returns to trading with those nations on WTO rules if they are a WTO member, or simply has no trade agreement with them at all if they are not.
The UK cannot keep EU trade deals as they all only apply to EU member states. As they were negotiated on the basis of EU rules that the UK would no longer be subject to and thus free to deviate from, and because the UK would be in a relatively weak and desperate position regarding the need for trade deals to reduce damage to its economy, it is unlikely that many countries would offer to quickly re-establish the same deals.
The UK government has managed to get some replacement deals in place with smaller nations, the largest (economically) of which is Switzerland. No bigger economies, such as the US, Japan, the EU itself, Australia, Canada, Brazil, India etc, have signed on and appear to be waiting for the situation to favour them as outlined above.