Half way through root canal. Loads of pain & now tooth has cracked vertically ... What will dentist do now??!!??

OMG are you the Dentist!!

They will exttract the tooth, be cause a vertical fracture is non-restorable.

l think u mean that u had the first half of the root canal done & u r waiting to go back for the second. The breaking is common, when u have a RTC it weakens the tooth, u should have been advised not to chew on that side till the final restoration was completed. Without seeing how severe the break is & how much tooth is left l can not tell u what will need to be done. You really need to give a little more information.
Were u planning on having a crown done after the RTC or just having the acess hole filled? If u planned on a crown & now the tooth broke, u may still be able to have a crown put on, with a little bit of crown lengthening(this is when they cut away some of the gums to expose more of the tooth) & a crown build up(this is when they put a post into the root canal, then build up the missing part of the tooth with a plastic resin material)
If the entire tooth WAS still in tact prior to the RTC & u just needed the access hole filled, but now the crack happened, You may NOW be in need of a crown.
If basically all the tooth is gone & it is flush with the gums u may need to have the rest of the tooth extracted & have an implant placed in the empty space. There r so many senarios.
It is really hard to tell. l could help u better if u answered these questions:
Is it a molar or a front tooth?
Is it a crack u can see in the light, or an actual break where a piece fell off?
How much of the tooth is left?
Is it sensitive to cold? hot? or both?
Is ur face swollen?
Hope l helped or maybe educated u a little
l also hope l did not confuse or scare you!
GOOD LUCK!!!

by-by tooth, hello bridge

The dentist l work for waits until the tooth dies to do the root canal. If he thought the tooth was cracked, he would not do a root canal. The reason behind this is that u have to crown (or do a large filling) a tooth after a root canal is done, but if it is cracked, u will always have leakage even after the crown is placed. He says, ''If a glass jar is cracked, u can still put the lid on but not completely seal it.'' Just another point of view for you. You will likely have to have it pulled. Sorry.