Rebels either need to take and hold your capital for 2 years OR occupy more than 50% (66%?) of your country.
Being at war prevents the collapse of your nation, but not defection of provinces due to patriots, zeals and alike.
The exact effects of sucessful rebels vary from rebel type to rebel type and can be looked up in EU3\common\rebel_types.txt.
Look out for the command "demands_enforced_effect = {". Effects of negotiation are listed under "demands_accepted_effect = {", effects of victorious sieges are listed in "siege_won_effect = {".
In addition, some rebel types transfer their troops to your nation if they can enforce their demands (like pretenders, so letting them win can actually be good sometimes!). Look for "unit_transfer =" right under the rebel type designation.
Being at war prevents the collapse of your nation, but not defection of provinces due to patriots, zeals and alike.
The exact effects of sucessful rebels vary from rebel type to rebel type and can be looked up in EU3\common\rebel_types.txt.
Look out for the command "demands_enforced_effect = {". Effects of negotiation are listed under "demands_accepted_effect = {", effects of victorious sieges are listed in "siege_won_effect = {".
In addition, some rebel types transfer their troops to your nation if they can enforce their demands (like pretenders, so letting them win can actually be good sometimes!). Look for "unit_transfer =" right under the rebel type designation.