It’s certainly possibly. Any game that does multi resolution / off screen particles creates a proper premultiplied render texture for compositing back into the main camera. The trick is usually you need to use custom particle shaders with properly setup blend states for the alpha rather than using the same blend as color.
For example, using Unity, if you have a traditional alpha shader, you need to use this blend mode:
Blend SrcAlpha OneMinusSrcAlpha, One OneMinusSrcAlpha
Additive shaders should use this:
Blend One One, Zero One
Blend SrcAlpha One, Zero One
And premultiplied shaders don’t need anything at all as they already work properly.
The other option is you can render out the effect with a white and black background at the same time and use the difference to calculate an alpha mask. It’s not perfect, but there used to be an asset on the unity asset store that used this technique to generate flipbooks from in game effects. You just need to cameras in the same spot with the different background colors, both rendering to a render texture, and output the black background as the color and dot(1 + (black.rgb - white.rgb), float3(1/3,1/3,1/3)) as the alpha.