A vote for repeal will not create a legal vacuum. The current legislation (the Protection of Life During Pregnancy Act 2013) will continue to operate until a new law for the regulation of abortion is introduced.
At the moment Irish abortion law is made up of both Article 40.3.3 (‘the 8th Amendment’) of the Constitution, and the Protection of Life During Pregnancy Act 2013 (see explanation here). If the People vote ‘yes’ on May 25th, Article 40.3.3 will be repealed and replaced with a text that empowers the Oireachtas to introduce new abortion law (see the explanation here). However, the Protection of Life During Pregnancy Act 2013 will remain in force until new legislation is enacted.
As long as the Protection of Life During Pregnancy Act 2013 remains in place, pregnant people will still be able to access abortion as a last resort where their lives are at ‘real and substantial’ risk and the foetus is not yet viable. In all other cases, pregnant people seeking abortion will most likely continue to travel for abortion or to import the abortion pill. Importing and taking the abortion pill to self-administer an abortion will remain a crime for as long as the Protection of Life During Pregnancy Act 2013 is in force.
Repeal of the 8th will not result in a legal vacuum. The Protection of Life During Pregnancy Act 2013 will continue to operate unless and until it is repealed and replaced by a new law, passed by the Oireachtas.
Edit: of course the constitutionality of the Protection of Life During Pregnancy Act 2013 might be challenged at any time (now or after the referendum). If it were found to be unconstitutional part of all of it could be struck down. We consider this possibility here. This is a normal/everyday part of the operation of constitutional law in Ireland.