Melanoma stage 4 timeline

Hi 

diagnosed melanoma stage 4 last year from back mole removed  had neck dissection and lymph removal now been on immunotherapy 1 year .  Metastatic spread to lungs liver adrenal and bones which the immunotherapy is keeping stable but what happens next year when 2 year treatment is complete ? Anyone had any experience? What is life expectancy? Trying to remain positive but need to make some financial life choices in near future so looking for a bit insight ? Thanks