I think I will order a right bladder just to have at my disposal. Me and sinking don't work good together.
My experience over more than 30 years is that sinking is extremely rare, the closest I've read or heard about is something like a quick large puncture. When the pressure goes out thru a puncture, air pockets are usually trapped in folds sections away from the puncture, which provide some floatation, if there is only a single bladder. There won't be a sinking unless there is something very heavy securely tied to the float tube- like maybe a battery/troll motor- to drag it down. A man can use a punctured float tube to help reach shore or to stay afloat until help arrives if the water is not too cold.
My float tube is kept at low pressure, just enough to hold shape and then topped off with a mouth tube just before launching. This helps it last longer, because there is less stress on the bladder and fabric seams compared to storage at full pressure- plus hot days can make the full pressure go over recommendations.
I usually buy at least 2 float tubes of the same kind at the lowest price I can get. That way I have a backup to use while I test any bladder repairs under pressure over a week or so. Usually saves time waiting for parts to arrive and saves money as the complete boat usually costs less on sale than the individual bladders purchased separately. The spare can also be used for its other parts or for a fishing buddy.
Hope this helps.