If your Dantian is slowly damaged, then the injury won't be as severe as you imagine.
After all, the Dantian has its own self-healing properties. A slowly damaged Dantian can heal itself while being damaged, so although the damage process seems dire, it is not as severe as imagined.
Of course, this excludes injuries like Dantian perforation or Dantian tearing.
However, an instant damage would mean directly piercing a big hole in your Dantian or even evaporating part of the inner wall of the Dantian. This kind of situation would cause the Dantian's injury to be very severe because instant perforation or direct evaporation of some of the Dantian's inner walls would lead to a rapid chaos of Spiritual Power within the Dantian.
The Spiritual Power in the Dantian is under intense compression, but if the Dantian is directly pierced or some of the inner walls evaporated, this pressure would disappear.
