In case it helps, the float filter takes an option parameter which is the value it should return if it can’t interpret its input. So, e.g.,
{{ states('sensor.does_not_exist')|float(1) }}
Would result in 1. This is because the states() function returns 'unknown', and that cannot be interpreted as a number, so float(1) returns the default value passed in, which in this case is 1. Same would happen for 'unavailable'.