The first card we drew is the reversed Ten of Cups. This card represents the ideal of health and good fortune. When this card appears in reverse, it indicates that you must be aware that things will not always go as you expect and that health is not guaranteed, but work must be done to obtain the most desired health. Furthermore, this card can also indicate that one wants too much of oneself with respect to their health and enough effort to maintain it.
The second card drawn is The Star reversed. This card represents acceptance of the current situation and health restrictions. When this card appears upside down, it indicates that you must accept your health conditions, even if they are not the desired ones. It can also mean that you have to learn to live with your health limitations and be content with what you have.
In conclusion, the tarot suggests that your cousin had a great stroke of luck having been in a car accident and coming out unscathed. However, that doesn't necessarily mean you'll have the same luck. You must consider your efforts to maintain ideal health and accept the limitations associated with your health. So, the most likely answer to your question is No; you cannot just rely on luck to maintain your health as you have to work hard to achieve the goal and accept limitations when necessary.