Li Shenron
Legend
With so many healing and self-healing options to many classes, I seriously doubt that you specifically need a Cleric to play the game.
It is OK if having a Cleric allows for a little bit more combat in a day, just like having a Fighter or Evoker Wizard or another class more combat-oriented than exploration-oriented or interaction-oriented would also do. But if the difference was so large that you had to start playing adventures of a lower level, then there would be a serious design issue in the edition!
The Cleric has other very useful capabilities, such as removing short-term and long-term negative effects from party members. But this is similar for all classes... if you don't have a Cleric you are more vulnerable to diseases, curses, poison etc., if you don't have a Rogue you are more vulnerable to traps and to missing useful stuff in secret or locked areas, if you don't have a Ranger you are more vulnerable to wilderness hazards, if you don't have a Paladin you are more vulnerable to fiends and undead and so on... This is part of the game and it's a good thing! It's a strategic choice when forming a party. If you don't like being vulnerable in any area, there are workarounds (skills, feats, multiclassing, magic items...), or the DM can adjust the adventures for you in order to de-emphasize the dangers you are more vulnerable against.
It is OK if having a Cleric allows for a little bit more combat in a day, just like having a Fighter or Evoker Wizard or another class more combat-oriented than exploration-oriented or interaction-oriented would also do. But if the difference was so large that you had to start playing adventures of a lower level, then there would be a serious design issue in the edition!
The Cleric has other very useful capabilities, such as removing short-term and long-term negative effects from party members. But this is similar for all classes... if you don't have a Cleric you are more vulnerable to diseases, curses, poison etc., if you don't have a Rogue you are more vulnerable to traps and to missing useful stuff in secret or locked areas, if you don't have a Ranger you are more vulnerable to wilderness hazards, if you don't have a Paladin you are more vulnerable to fiends and undead and so on... This is part of the game and it's a good thing! It's a strategic choice when forming a party. If you don't like being vulnerable in any area, there are workarounds (skills, feats, multiclassing, magic items...), or the DM can adjust the adventures for you in order to de-emphasize the dangers you are more vulnerable against.