I apologize because I made it into a complicated thing. It's needed some mood choice there that surely stumps the advanced student.
Vienes/venís al mundo llorando mientras los que están a tu lado sonríen...(* came back here when you read further)
so far, indicative as those actions are real, are happening, are given as the truth.
Vive/viví tu vida
de modo que (this tells that what follows is an adverbial clause) lo abandones/dejes sonriendo mientras los que
están a tu lado
lloran
Those emphasized instances of indicative (the Spanish one, not the English one; two different things) may -and should- cause some hesitation to the intermediate and advance studence, as it's an adverbial clause.
The key is "mientras" which is used to construct both
cláusulas suspensivas and to describe simultaneous actions.
I'll explain it -overexplain?- in detail. Short-cuts and working around this are all over the web and Spanish courses -which are useful to start training the "subjunctive" muscle in students, but aren't the real McKay/McCoy-
"... lo abandones/dejes sonriendo..." ---> undoubtedly subjunctive, not because you are still alive; not because what's been described hasn't happened yet; not because you may die in different circumstances; not because you're grammatically rubbing a rabbit leg or knocking on wood to keep death away. Subjunctive because it's an adverbial clause subordinated to the main notion "they way you should live your life so you achieve what follows".
But then, a few options follow, with different meaning -sometimes no subtle at all-
"... mientras los que estén a tu lado lloren." ---> the whole thing is a bit ambiguous for the native speaker with elementary education, but basically suggests you should agonize with one eye open, and when you perceive some group near you crying, then you smile and check-out. Many may tell you otherwise because they reject the harsh notion -which I purposely expressed in the most heartless way possible- and not what the grammar
really tells. Remember that basically the subjunctive mood denies actions (normal language: Ve! ....No ve! Spanish: ¡Ve! ...¡No vayas!) and there's a temptation in the speaker to tone down the description of the act of dying by dropping more subjunctive instances than those correct. No harm in that. All of us hate death, and we hate most the death of those who we love than ours, so saying "this is not happening... this is not going to happen" is not grammar: it's human. [* indicative, not only because that happens, but because it's a welcome source of joy
. Magical thinking is also hidden in the way Spanish expresses.]
"...mientras los que estén a tu lado lloran" ---> indicative forced over subjunctive tells what is depicted shall happen, because it must to complete the command in the phrase. That's the evidence you lived a worthy and meaningful life and that you are to take the lift up having grown the most. However, that
estén describes a circumstance around the act of dying, and the notion should be complete, so we force subjunctive into indicative because we have no doubt a lot of kin and friends will be around:
"...mientras los que están a tu lado lloran" makes the whole thing into a maxim; a saying; a moral; a mouthful; a command on how we should live our existence.
Hope this helps.