Do you bleed to death after your penis is cut off?

The problem is there are too many unknowns. First, the speed of clotting varies from person to person. There are lab tests that measure clotting time (e.g. INR), especially useful when a patient takes anticoagulants. One respondent mentioned the absence of anticoagulants, but anticoagulants include substances not specifically prescribed to reduce clotting, such as supplements and even food items that reduce clotting. Further, there are genetic factors (i.e. Factor VIII and others) that modulate clotting time, operating independently of medical intervention/prescribed drugs or anything consumed. Age is another facet in the clotting process, as infants often do not clot quickly. Couple that fact with the smaller quantity of blood in an infant's body and it makes sense why some infants actually die from circumcision related bleeding. An infant may retain his penis after circumcision but still die from operation related blood loss.

Additionally, the penis is different than other appendages and extremities. Besides the difference in tissue composition (smooth muscle vs. skeletal muscle elsewhere), penile arteries dilate more than arteries elsewhere and veins constrict more than veins elsewhere (assuming one has generally healthy blood vessels prior to injury). The unique elasticity of penile blood vessels mean that a traumatic injury like penile amputation is more likely to bleed continuously than many other amputations when taking into account the relative area of tissue amputated and blood vessels severed. Other than the femoral or carotid arteries, which, due to their own unique locations, are more likely to cause death from dissection than severing other arteries, the penis is again unique in that the arteries both inside and leading to it do not always clamp off- sometimes, they remain dilated even after a severing injury.

One of the biggest factors of survival (a somewhat controllable factor) in this case is time. The more time elapses after amputation without subsequent medical intervention, the more likely death becomes.

Death from penile amputation can arise not simply from blood loss but also from related issues such as overall stress and pain. Stress hormones and an inflammatory chemical cascade following such a traumatic injury can overwhelm the heart.

Assuming the person is not taking anticoagulants, it's actually quite difficult to bleed to death from dismemberment of small members (hands, feet, penis, ears, nose, etc). Even large members such as arms and legs are often survivable because the body is very good at protecting itself from blood loss. For example, transected arteries will spasm and clamp off blood flow, and loss of blood will cause the body to divert blood flow away from the extremities and to the vital organs, thereby slowing the bleeding and allowing it to clot. In fact, the whole shock process can be viewed as a set of defensive measures by the body to ensure survival in the face of serious injury. This was a bitter lesson learned by emergency medicine only fairly recently. The standard practice used to be to infuse hypovolemic patients with fluids to maintain normal blood pressure. The trouble is, a normal blood pressure prevents the body from realizing it has inadequate blood volume and turns off its defensive measures, thus allowing the bleeding to continue unabated.

Left to fend for himself, a healthy adult would almost certainly survive having his penis removed. With modern medical care, that becomes a certainty.

Could he still urinate? Sure, as long as the urethra wasn't blocked. It could become blocked by clotted blood, but eventually the pressure of a full bladder would overcome the blockage.